[linux-2.6.git] / mm / mmap.c

/*
 * mm/mmap.c
 *
 * Written by obz.
 *
 * Address space accounting code        <alan@redhat.com>
 */

#include <linux/slab.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/init.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/hugetlb.h>
#include <linux/profile.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>

#include <asm/uaccess.h>
#include <asm/pgalloc.h>
#include <asm/cacheflush.h>
#include <asm/tlb.h>

/*
 * WARNING: the debugging will use recursive algorithms so never enable this
 * unless you know what you are doing.
 */
#undef DEBUG_MM_RB

/* description of effects of mapping type and prot in current implementation.
 * this is due to the limited x86 page protection hardware.  The expected
 * behavior is in parens:
 *
 * map_type     prot
 *              PROT_NONE       PROT_READ       PROT_WRITE      PROT_EXEC
 * MAP_SHARED   r: (no) no      r: (yes) yes    r: (no) yes     r: (no) yes
 *              w: (no) no      w: (no) no      w: (yes) yes    w: (no) no
 *              x: (no) no      x: (no) yes     x: (no) yes     x: (yes) yes
 *              
 * MAP_PRIVATE  r: (no) no      r: (yes) yes    r: (no) yes     r: (no) yes
 *              w: (no) no      w: (no) no      w: (copy) copy  w: (no) no
 *              x: (no) no      x: (no) yes     x: (no) yes     x: (yes) yes
 *
 */
pgprot_t protection_map[16] = {
        __P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
        __S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
};

int sysctl_overcommit_memory = 0;       /* default is heuristic overcommit */
int sysctl_overcommit_ratio = 50;       /* default is 50% */
int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
atomic_t vm_committed_space = ATOMIC_INIT(0);

EXPORT_SYMBOL(sysctl_overcommit_memory);
EXPORT_SYMBOL(sysctl_overcommit_ratio);
EXPORT_SYMBOL(sysctl_max_map_count);
EXPORT_SYMBOL(vm_committed_space);

/*
 * Requires inode->i_mapping->i_mmap_lock
 */
static void __remove_shared_vm_struct(struct vm_area_struct *vma,
                struct file *file, struct address_space *mapping)
{
        if (vma->vm_flags & VM_DENYWRITE)
                atomic_inc(&file->f_dentry->d_inode->i_writecount);
        if (vma->vm_flags & VM_SHARED)
                mapping->i_mmap_writable--;

        flush_dcache_mmap_lock(mapping);
        if (unlikely(vma->vm_flags & VM_NONLINEAR))
                list_del_init(&vma->shared.vm_set.list);
        else
                vma_prio_tree_remove(vma, &mapping->i_mmap);
        flush_dcache_mmap_unlock(mapping);
}

/*
 * Remove one vm structure and free it.
 */
static void remove_vm_struct(struct vm_area_struct *vma)
{
        struct file *file = vma->vm_file;

        if (file) {
                struct address_space *mapping = file->f_mapping;
                spin_lock(&mapping->i_mmap_lock);
                __remove_shared_vm_struct(vma, file, mapping);
                spin_unlock(&mapping->i_mmap_lock);
        }
        if (vma->vm_ops && vma->vm_ops->close)
                vma->vm_ops->close(vma);
        if (file)
                fput(file);
        anon_vma_unlink(vma);
        mpol_free(vma_policy(vma));
        kmem_cache_free(vm_area_cachep, vma);
}

/*
 *  sys_brk() for the most part doesn't need the global kernel
 *  lock, except when an application is doing something nasty
 *  like trying to un-brk an area that has already been mapped
 *  to a regular file.  in this case, the unmapping will need
 *  to invoke file system routines that need the global lock.
 */
asmlinkage unsigned long sys_brk(unsigned long brk)
{
        unsigned long rlim, retval;
        unsigned long newbrk, oldbrk;
        struct mm_struct *mm = current->mm;

        down_write(&mm->mmap_sem);

        if (brk < mm->end_code)
                goto out;
        newbrk = PAGE_ALIGN(brk);
        oldbrk = PAGE_ALIGN(mm->brk);
        if (oldbrk == newbrk)
                goto set_brk;

        /* Always allow shrinking brk. */
        if (brk <= mm->brk) {
                if (!do_munmap(mm, newbrk, oldbrk-newbrk))
                        goto set_brk;
                goto out;
        }

        /* Check against rlimit.. */
        rlim = current->rlim[RLIMIT_DATA].rlim_cur;
        if (rlim < RLIM_INFINITY && brk - mm->start_data > rlim)
                goto out;

        /* Check against existing mmap mappings. */
        if (find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE))
                goto out;

        /* Ok, looks good - let it rip. */
        if (do_brk(oldbrk, newbrk-oldbrk) != oldbrk)
                goto out;
set_brk:
        mm->brk = brk;
out:
        retval = mm->brk;
        up_write(&mm->mmap_sem);
        return retval;
}

#ifdef DEBUG_MM_RB
static int browse_rb(struct rb_root *root)
{
        int i = 0, j;
        struct rb_node *nd, *pn = NULL;
        unsigned long prev = 0, pend = 0;

        for (nd = rb_first(root); nd; nd = rb_next(nd)) {
                struct vm_area_struct *vma;
                vma = rb_entry(nd, struct vm_area_struct, vm_rb);
                if (vma->vm_start < prev)
                        printk("vm_start %lx prev %lx\n", vma->vm_start, prev), i = -1;
                if (vma->vm_start < pend)
                        printk("vm_start %lx pend %lx\n", vma->vm_start, pend);
                if (vma->vm_start > vma->vm_end)
                        printk("vm_end %lx < vm_start %lx\n", vma->vm_end, vma->vm_start);
                i++;
                pn = nd;
        }
        j = 0;
        for (nd = pn; nd; nd = rb_prev(nd)) {
                j++;
        }
        if (i != j)
                printk("backwards %d, forwards %d\n", j, i), i = 0;
        return i;
}

void validate_mm(struct mm_struct *mm)
{
        int bug = 0;
        int i = 0;
        struct vm_area_struct *tmp = mm->mmap;
        while (tmp) {
                tmp = tmp->vm_next;
                i++;
        }
        if (i != mm->map_count)
                printk("map_count %d vm_next %d\n", mm->map_count, i), bug = 1;
        i = browse_rb(&mm->mm_rb);
        if (i != mm->map_count)
                printk("map_count %d rb %d\n", mm->map_count, i), bug = 1;
        if (bug)
                BUG();
}
#else
#define validate_mm(mm) do { } while (0)
#endif

static struct vm_area_struct *
find_vma_prepare(struct mm_struct *mm, unsigned long addr,
                struct vm_area_struct **pprev, struct rb_node ***rb_link,
                struct rb_node ** rb_parent)
{
        struct vm_area_struct * vma;
        struct rb_node ** __rb_link, * __rb_parent, * rb_prev;

        __rb_link = &mm->mm_rb.rb_node;
        rb_prev = __rb_parent = NULL;
        vma = NULL;

        while (*__rb_link) {
                struct vm_area_struct *vma_tmp;

                __rb_parent = *__rb_link;
                vma_tmp = rb_entry(__rb_parent, struct vm_area_struct, vm_rb);

                if (vma_tmp->vm_end > addr) {
                        vma = vma_tmp;
                        if (vma_tmp->vm_start <= addr)
                                return vma;
                        __rb_link = &__rb_parent->rb_left;
                } else {
                        rb_prev = __rb_parent;
                        __rb_link = &__rb_parent->rb_right;
                }
        }

        *pprev = NULL;
        if (rb_prev)
                *pprev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
        *rb_link = __rb_link;
        *rb_parent = __rb_parent;
        return vma;
}

static inline void
__vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
                struct vm_area_struct *prev, struct rb_node *rb_parent)
{
        if (vma->vm_flags & VM_EXEC)
                arch_add_exec_range(mm, vma->vm_end);
        if (prev) {
                vma->vm_next = prev->vm_next;
                prev->vm_next = vma;
        } else {
                mm->mmap = vma;
                if (rb_parent)
                        vma->vm_next = rb_entry(rb_parent,
                                        struct vm_area_struct, vm_rb);
                else
                        vma->vm_next = NULL;
        }
}

void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
                struct rb_node **rb_link, struct rb_node *rb_parent)
{
        rb_link_node(&vma->vm_rb, rb_parent, rb_link);
        rb_insert_color(&vma->vm_rb, &mm->mm_rb);
}

static inline void __vma_link_file(struct vm_area_struct *vma)
{
        struct file * file;

        file = vma->vm_file;
        if (file) {
                struct address_space *mapping = file->f_mapping;

                if (vma->vm_flags & VM_DENYWRITE)
                        atomic_dec(&file->f_dentry->d_inode->i_writecount);
                if (vma->vm_flags & VM_SHARED)
                        mapping->i_mmap_writable++;

                flush_dcache_mmap_lock(mapping);
                if (unlikely(vma->vm_flags & VM_NONLINEAR))
                        list_add_tail(&vma->shared.vm_set.list,
                                        &mapping->i_mmap_nonlinear);
                else
                        vma_prio_tree_insert(vma, &mapping->i_mmap);
                flush_dcache_mmap_unlock(mapping);
        }
}

static void
__vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
        struct vm_area_struct *prev, struct rb_node **rb_link,
        struct rb_node *rb_parent)
{
        vma_prio_tree_init(vma);
        __vma_link_list(mm, vma, prev, rb_parent);
        __vma_link_rb(mm, vma, rb_link, rb_parent);
        __vma_link_file(vma);
        __anon_vma_link(vma);
}

static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
                        struct vm_area_struct *prev, struct rb_node **rb_link,
                        struct rb_node *rb_parent)
{
        struct address_space *mapping = NULL;

        if (vma->vm_file)
                mapping = vma->vm_file->f_mapping;

        if (mapping)
                spin_lock(&mapping->i_mmap_lock);
        anon_vma_lock(vma);
        __vma_link(mm, vma, prev, rb_link, rb_parent);
        anon_vma_unlock(vma);
        if (mapping)
                spin_unlock(&mapping->i_mmap_lock);

        mark_mm_hugetlb(mm, vma);
        mm->map_count++;
        validate_mm(mm);
}

/*
 * Insert vm structure into process list sorted by address and into the
 * inode's i_mmap tree. The caller should hold mm->mmap_sem and
 * ->f_mappping->i_mmap_lock if vm_file is non-NULL.
 */
static void
__insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
{
        struct vm_area_struct * __vma, * prev;
        struct rb_node ** rb_link, * rb_parent;

        __vma = find_vma_prepare(mm, vma->vm_start,&prev, &rb_link, &rb_parent);
        if (__vma && __vma->vm_start < vma->vm_end)
                BUG();
        __vma_link(mm, vma, prev, rb_link, rb_parent);
        mark_mm_hugetlb(mm, vma);
        mm->map_count++;
        validate_mm(mm);
}

static inline void
__vma_unlink(struct mm_struct *mm, struct vm_area_struct *vma,
                struct vm_area_struct *prev)
{
        prev->vm_next = vma->vm_next;
        rb_erase(&vma->vm_rb, &mm->mm_rb);
        if (mm->mmap_cache == vma)
                mm->mmap_cache = prev;
        if (vma->vm_flags & VM_EXEC)
                arch_remove_exec_range(mm, vma->vm_end);
}

/*
 * We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
 * is already present in an i_mmap tree without adjusting the tree.
 * The following helper function should be used when such adjustments
 * are necessary.  The "insert" vma (if any) is to be inserted
 * before we drop the necessary locks.
 */
void vma_adjust(struct vm_area_struct *vma, unsigned long start,
        unsigned long end, pgoff_t pgoff, struct vm_area_struct *insert)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *next = vma->vm_next;
        struct address_space *mapping = NULL;
        struct prio_tree_root *root = NULL;
        struct file *file = vma->vm_file;
        struct anon_vma *anon_vma = NULL;
        long adjust_next = 0;
        int remove_next = 0;

        if (next && !insert) {
                if (end >= next->vm_end) {
again:                  remove_next = 1 + (end > next->vm_end);
                        end = next->vm_end;
                        anon_vma = next->anon_vma;
                } else if (end < vma->vm_end || end > next->vm_start) {
                        /*
                         * vma shrinks, and !insert tells it's not
                         * split_vma inserting another: so it must
                         * be mprotect shifting the boundary down.
                         *   Or:
                         * vma expands, overlapping part of the next:
                         * must be mprotect shifting the boundary up.
                         */
                        BUG_ON(vma->vm_end != next->vm_start);
                        adjust_next = end - next->vm_start;
                        anon_vma = next->anon_vma;
                }
        }

        if (file) {
                mapping = file->f_mapping;
                if (!(vma->vm_flags & VM_NONLINEAR))
                        root = &mapping->i_mmap;
                spin_lock(&mapping->i_mmap_lock);
        }

        /*
         * When changing only vma->vm_end, we don't really need
         * anon_vma lock: but is that case worth optimizing out?
         */
        if (vma->anon_vma)
                anon_vma = vma->anon_vma;
        if (anon_vma)
                spin_lock(&anon_vma->lock);

        if (root) {
                flush_dcache_mmap_lock(mapping);
                vma_prio_tree_remove(vma, root);
                if (adjust_next)
                        vma_prio_tree_remove(next, root);
        }

        vma->vm_start = start;
        vma->vm_end = end;
        vma->vm_pgoff = pgoff;
        if (adjust_next) {
                next->vm_start += adjust_next;
                next->vm_pgoff += adjust_next >> PAGE_SHIFT;
        }

        if (root) {
                if (adjust_next) {
                        vma_prio_tree_init(next);
                        vma_prio_tree_insert(next, root);
                }
                vma_prio_tree_init(vma);
                vma_prio_tree_insert(vma, root);
                flush_dcache_mmap_unlock(mapping);
        }

        if (remove_next) {
                /*
                 * vma_merge has merged next into vma, and needs
                 * us to remove next before dropping the locks.
                 */
                __vma_unlink(mm, next, vma);
                if (file)
                        __remove_shared_vm_struct(next, file, mapping);
                if (next->anon_vma)
                        __anon_vma_merge(vma, next);
        } else if (insert) {
                /*
                 * split_vma has split insert from vma, and needs
                 * us to insert it before dropping the locks
                 * (it may either follow vma or precede it).
                 */
                __insert_vm_struct(mm, insert);
        }

        if (anon_vma)
                spin_unlock(&anon_vma->lock);
        if (mapping)
                spin_unlock(&mapping->i_mmap_lock);

        if (remove_next) {
                if (file)
                        fput(file);
                mm->map_count--;
                mpol_free(vma_policy(next));
                kmem_cache_free(vm_area_cachep, next);
                /*
                 * In mprotect's case 6 (see comments on vma_merge),
                 * we must remove another next too. It would clutter
                 * up the code too much to do both in one go.
                 */
                if (remove_next == 2) {
                        next = vma->vm_next;
                        goto again;
                }
        }

        validate_mm(mm);
}

/*
 * If the vma has a ->close operation then the driver probably needs to release
 * per-vma resources, so we don't attempt to merge those.
 */
#define VM_SPECIAL (VM_IO | VM_DONTCOPY | VM_DONTEXPAND | VM_RESERVED)

static inline int is_mergeable_vma(struct vm_area_struct *vma,
                        struct file *file, unsigned long vm_flags)
{
        if (vma->vm_flags != vm_flags)
                return 0;
        if (vma->vm_file != file)
                return 0;
        if (vma->vm_ops && vma->vm_ops->close)
                return 0;
        return 1;
}

static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
                                        struct anon_vma *anon_vma2)
{
        return !anon_vma1 || !anon_vma2 || (anon_vma1 == anon_vma2);
}

/*
 * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
 * in front of (at a lower virtual address and file offset than) the vma.
 *
 * We cannot merge two vmas if they have differently assigned (non-NULL)
 * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
 *
 * We don't check here for the merged mmap wrapping around the end of pagecache
 * indices (16TB on ia32) because do_mmap_pgoff() does not permit mmap's which
 * wrap, nor mmaps which cover the final page at index -1UL.
 */
static int
can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
        struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
{
        if (is_mergeable_vma(vma, file, vm_flags) &&
            is_mergeable_anon_vma(anon_vma, vma->anon_vma)) {
                if (vma->vm_pgoff == vm_pgoff)
                        return 1;
        }
        return 0;
}

/*
 * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
 * beyond (at a higher virtual address and file offset than) the vma.
 *
 * We cannot merge two vmas if they have differently assigned (non-NULL)
 * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
 */
static int
can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
        struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
{
        if (is_mergeable_vma(vma, file, vm_flags) &&
            is_mergeable_anon_vma(anon_vma, vma->anon_vma)) {
                pgoff_t vm_pglen;
                vm_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
                if (vma->vm_pgoff + vm_pglen == vm_pgoff)
                        return 1;
        }
        return 0;
}

/*
 * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
 * whether that can be merged with its predecessor or its successor.
 * Or both (it neatly fills a hole).
 *
 * In most cases - when called for mmap, brk or mremap - [addr,end) is
 * certain not to be mapped by the time vma_merge is called; but when
 * called for mprotect, it is certain to be already mapped (either at
 * an offset within prev, or at the start of next), and the flags of
 * this area are about to be changed to vm_flags - and the no-change
 * case has already been eliminated.
 *
 * The following mprotect cases have to be considered, where AAAA is
 * the area passed down from mprotect_fixup, never extending beyond one
 * vma, PPPPPP is the prev vma specified, and NNNNNN the next vma after:
 *
 *     AAAA             AAAA                AAAA          AAAA
 *    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPNNNNXXXX
 *    cannot merge    might become    might become    might become
 *                    PPNNNNNNNNNN    PPPPPPPPPPNN    PPPPPPPPPPPP 6 or
 *    mmap, brk or    case 4 below    case 5 below    PPPPPPPPXXXX 7 or
 *    mremap move:                                    PPPPNNNNNNNN 8
 *        AAAA
 *    PPPP    NNNN    PPPPPPPPPPPP    PPPPPPPPNNNN    PPPPNNNNNNNN
 *    might become    case 1 below    case 2 below    case 3 below
 *
 * Odd one out? Case 8, because it extends NNNN but needs flags of XXXX:
 * mprotect_fixup updates vm_flags & vm_page_prot on successful return.
 */
struct vm_area_struct *vma_merge(struct mm_struct *mm,
                        struct vm_area_struct *prev, unsigned long addr,
                        unsigned long end, unsigned long vm_flags,
                        struct anon_vma *anon_vma, struct file *file,
                        pgoff_t pgoff, struct mempolicy *policy)
{
        pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
        struct vm_area_struct *area, *next;

        /*
         * We later require that vma->vm_flags == vm_flags,
         * so this tests vma->vm_flags & VM_SPECIAL, too.
         */
        if (vm_flags & VM_SPECIAL)
                return NULL;

        if (prev)
                next = prev->vm_next;
        else
                next = mm->mmap;
        area = next;
        if (next && next->vm_end == end)                /* cases 6, 7, 8 */
                next = next->vm_next;

        /*
         * Can it merge with the predecessor?
         */
        if (prev && prev->vm_end == addr &&
                        mpol_equal(vma_policy(prev), policy) &&
                        can_vma_merge_after(prev, vm_flags,
                                                anon_vma, file, pgoff)) {
                /*
                 * OK, it can.  Can we now merge in the successor as well?
                 */
                if (next && end == next->vm_start &&
                                mpol_equal(policy, vma_policy(next)) &&
                                can_vma_merge_before(next, vm_flags,
                                        anon_vma, file, pgoff+pglen) &&
                                is_mergeable_anon_vma(prev->anon_vma,
                                                      next->anon_vma)) {
                                                        /* cases 1, 6 */
                        vma_adjust(prev, prev->vm_start,
                                next->vm_end, prev->vm_pgoff, NULL);
                } else                                  /* cases 2, 5, 7 */
                        vma_adjust(prev, prev->vm_start,
                                end, prev->vm_pgoff, NULL);
                if (prev->vm_flags & VM_EXEC)
                        arch_add_exec_range(mm, prev->vm_end);
                return prev;
        }

        /*
         * Can this new request be merged in front of next?
         */
        if (next && end == next->vm_start &&
                        mpol_equal(policy, vma_policy(next)) &&
                        can_vma_merge_before(next, vm_flags,
                                        anon_vma, file, pgoff+pglen)) {
                if (prev && addr < prev->vm_end)        /* case 4 */
                        vma_adjust(prev, prev->vm_start,
                                addr, prev->vm_pgoff, NULL);
                else                                    /* cases 3, 8 */
                        vma_adjust(area, addr, next->vm_end,
                                next->vm_pgoff - pglen, NULL);
                return area;
        }

        return NULL;
}

/*
 * find_mergeable_anon_vma is used by anon_vma_prepare, to check
 * neighbouring vmas for a suitable anon_vma, before it goes off
 * to allocate a new anon_vma.  It checks because a repetitive
 * sequence of mprotects and faults may otherwise lead to distinct
 * anon_vmas being allocated, preventing vma merge in subsequent
 * mprotect.
 */
struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
{
        struct vm_area_struct *near;
        unsigned long vm_flags;

        near = vma->vm_next;
        if (!near)
                goto try_prev;

        /*
         * Since only mprotect tries to remerge vmas, match flags
         * which might be mprotected into each other later on.
         * Neither mlock nor madvise tries to remerge at present,
         * so leave their flags as obstructing a merge.
         */
        vm_flags = vma->vm_flags & ~(VM_READ|VM_WRITE|VM_EXEC);
        vm_flags |= near->vm_flags & (VM_READ|VM_WRITE|VM_EXEC);

        if (near->anon_vma && vma->vm_end == near->vm_start &&
                        mpol_equal(vma_policy(vma), vma_policy(near)) &&
                        can_vma_merge_before(near, vm_flags,
                                NULL, vma->vm_file, vma->vm_pgoff +
                                ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT)))
                return near->anon_vma;
try_prev:
        /*
         * It is potentially slow to have to call find_vma_prev here.
         * But it's only on the first write fault on the vma, not
         * every time, and we could devise a way to avoid it later
         * (e.g. stash info in next's anon_vma_node when assigning
         * an anon_vma, or when trying vma_merge).  Another time.
         */
        if (find_vma_prev(vma->vm_mm, vma->vm_start, &near) != vma)
                BUG();
        if (!near)
                goto none;

        vm_flags = vma->vm_flags & ~(VM_READ|VM_WRITE|VM_EXEC);
        vm_flags |= near->vm_flags & (VM_READ|VM_WRITE|VM_EXEC);

        if (near->anon_vma && near->vm_end == vma->vm_start &&
                        mpol_equal(vma_policy(near), vma_policy(vma)) &&
                        can_vma_merge_after(near, vm_flags,
                                NULL, vma->vm_file, vma->vm_pgoff))
                return near->anon_vma;
none:
        /*
         * There's no absolute need to look only at touching neighbours:
         * we could search further afield for "compatible" anon_vmas.
         * But it would probably just be a waste of time searching,
         * or lead to too many vmas hanging off the same anon_vma.
         * We're trying to allow mprotect remerging later on,
         * not trying to minimize memory used for anon_vmas.
         */
        return NULL;
}

/*
 * The caller must hold down_write(current->mm->mmap_sem).
 */

unsigned long do_mmap_pgoff(struct mm_struct *mm, struct file * file, 
                            unsigned long addr, unsigned long len,
                            unsigned long prot, unsigned long flags,
                            unsigned long pgoff)
{
        struct vm_area_struct * vma, * prev;
        struct inode *inode;
        unsigned int vm_flags;
        int correct_wcount = 0;
        int error;
        struct rb_node ** rb_link, * rb_parent;
        int accountable = 1;
        unsigned long charged = 0;

        if (file) {
                if (is_file_hugepages(file))
                        accountable = 0;

                if (!file->f_op || !file->f_op->mmap)
                        return -ENODEV;

                if ((prot & PROT_EXEC) &&
                    (file->f_vfsmnt->mnt_flags & MNT_NOEXEC))
                        return -EPERM;
        }

        if (!len)
                return addr;

        /* Careful about overflows.. */
        len = PAGE_ALIGN(len);
        if (!len || len > TASK_SIZE)
                return -EINVAL;

        /* offset overflow? */
        if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
                return -EINVAL;

        /* Too many mappings? */
        if (mm->map_count > sysctl_max_map_count)
                return -ENOMEM;

        /* Obtain the address to map to. we verify (or select) it and ensure
         * that it represents a valid section of the address space.
         */
        addr = get_unmapped_area(file, addr, len, pgoff, flags, prot & PROT_EXEC);
        if (addr & ~PAGE_MASK)
                return addr;

        /* Do simple checking here so the lower-level routines won't have
         * to. we assume access permissions have been handled by the open
         * of the memory object, so we don't do any here.
         */
        vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags) |
                        mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

        if (flags & MAP_LOCKED) {
                if (!can_do_mlock())
                        return -EPERM;
                vm_flags |= VM_LOCKED;
        }
        /* mlock MCL_FUTURE? */
        if (vm_flags & VM_LOCKED) {
                unsigned long locked, lock_limit;
                locked = mm->locked_vm << PAGE_SHIFT;
                lock_limit = current->rlim[RLIMIT_MEMLOCK].rlim_cur;
                locked += len;
                if (locked > lock_limit && !capable(CAP_IPC_LOCK))
                        return -EAGAIN;
        }

        inode = file ? file->f_dentry->d_inode : NULL;

        if (file) {
                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
                                return -EACCES;

                        /*
                         * Make sure we don't allow writing to an append-only
                         * file..
                         */
                        if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
                                return -EACCES;

                        /*
                         * Make sure there are no mandatory locks on the file.
                         */
                        if (locks_verify_locked(inode))
                                return -EAGAIN;

                        vm_flags |= VM_SHARED | VM_MAYSHARE;
                        if (!(file->f_mode & FMODE_WRITE))
                                vm_flags &= ~(VM_MAYWRITE | VM_SHARED);

                        /* fall through */
                case MAP_PRIVATE:
                        if (!(file->f_mode & FMODE_READ))
                                return -EACCES;
                        break;

                default:
                        return -EINVAL;
                }
        } else {
                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        vm_flags |= VM_SHARED | VM_MAYSHARE;
                        break;
                case MAP_PRIVATE:
                        /*
                         * Set pgoff according to addr for anon_vma.
                         */
                        pgoff = addr >> PAGE_SHIFT;
                        break;
                default:
                        return -EINVAL;
                }
        }

        error = security_file_mmap(file, prot, flags);
        if (error)
                return error;
                
        /* Clear old maps */
        error = -ENOMEM;
munmap_back:
        vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
        if (vma && vma->vm_start < addr + len) {
                if (do_munmap(mm, addr, len))
                        return -ENOMEM;
                goto munmap_back;
        }

        /* Check against address space limit. */
        if ((mm->total_vm << PAGE_SHIFT) + len
            > current->rlim[RLIMIT_AS].rlim_cur)
                return -ENOMEM;

        /* check context space, maybe only Private writable mapping? */
        if (!vx_vmpages_avail(mm, len >> PAGE_SHIFT))
                return -ENOMEM;

        if (accountable && (!(flags & MAP_NORESERVE) ||
                        sysctl_overcommit_memory > 1)) {
                if (vm_flags & VM_SHARED) {
                        /* Check memory availability in shmem_file_setup? */
                        vm_flags |= VM_ACCOUNT;
                } else if (vm_flags & VM_WRITE) {
                        /*
                         * Private writable mapping: check memory availability
                         */
                        charged = len >> PAGE_SHIFT;
                        if (security_vm_enough_memory(charged))
                                return -ENOMEM;
                        vm_flags |= VM_ACCOUNT;
                }
        }

        /*
         * Can we just expand an old private anonymous mapping?
         * The VM_SHARED test is necessary because shmem_zero_setup
         * will create the file object for a shared anonymous map below.
         */
        if (!file && !(vm_flags & VM_SHARED) &&
            vma_merge(mm, prev, addr, addr + len, vm_flags,
                                        NULL, NULL, pgoff, NULL))
                goto out;

        /*
         * Determine the object being mapped and call the appropriate
         * specific mapper. the address has already been validated, but
         * not unmapped, but the maps are removed from the list.
         */
        vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
        if (!vma) {
                error = -ENOMEM;
                goto unacct_error;
        }
        memset(vma, 0, sizeof(*vma));

        vma->vm_mm = mm;
        vma->vm_start = addr;
        vma->vm_end = addr + len;
        vma->vm_flags = vm_flags;
        vma->vm_page_prot = protection_map[vm_flags & 0x0f];
        vma->vm_pgoff = pgoff;

        if (file) {
                error = -EINVAL;
                if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                        goto free_vma;
                if (vm_flags & VM_DENYWRITE) {
                        error = deny_write_access(file);
                        if (error)
                                goto free_vma;
                        correct_wcount = 1;
                }
                vma->vm_file = file;
                get_file(file);
                error = file->f_op->mmap(file, vma);
                if (error)
                        goto unmap_and_free_vma;
        } else if (vm_flags & VM_SHARED) {
                error = shmem_zero_setup(vma);
                if (error)
                        goto free_vma;
        }

        /* We set VM_ACCOUNT in a shared mapping's vm_flags, to inform
         * shmem_zero_setup (perhaps called through /dev/zero's ->mmap)
         * that memory reservation must be checked; but that reservation
         * belongs to shared memory object, not to vma: so now clear it.
         */
        if ((vm_flags & (VM_SHARED|VM_ACCOUNT)) == (VM_SHARED|VM_ACCOUNT))
                vma->vm_flags &= ~VM_ACCOUNT;

        /* Can addr have changed??
         *
         * Answer: Yes, several device drivers can do it in their
         *         f_op->mmap method. -DaveM
         */
        addr = vma->vm_start;

        if (!file || !vma_merge(mm, prev, addr, vma->vm_end,
                        vma->vm_flags, NULL, file, pgoff, vma_policy(vma))) {
                vma_link(mm, vma, prev, rb_link, rb_parent);
                if (correct_wcount)
                        atomic_inc(&inode->i_writecount);
        } else {
                if (file) {
                        if (correct_wcount)
                                atomic_inc(&inode->i_writecount);
                        fput(file);
                }
                mpol_free(vma_policy(vma));
                kmem_cache_free(vm_area_cachep, vma);
        }
out:    
        // mm->total_vm += len >> PAGE_SHIFT;
        vx_vmpages_add(mm, len >> PAGE_SHIFT);
        if (vm_flags & VM_LOCKED) {
                // mm->locked_vm += len >> PAGE_SHIFT;
                vx_vmlocked_add(mm, len >> PAGE_SHIFT);
                make_pages_present(addr, addr + len);
        }
        if (flags & MAP_POPULATE) {
                up_write(&mm->mmap_sem);
                sys_remap_file_pages(addr, len, 0,
                                        pgoff, flags & MAP_NONBLOCK);
                down_write(&mm->mmap_sem);
        }
        return addr;

unmap_and_free_vma:
        if (correct_wcount)
                atomic_inc(&inode->i_writecount);
        vma->vm_file = NULL;
        fput(file);

        /* Undo any partial mapping done by a device driver. */
        zap_page_range(vma, vma->vm_start, vma->vm_end - vma->vm_start, NULL);
free_vma:
        kmem_cache_free(vm_area_cachep, vma);
unacct_error:
        if (charged)
                vm_unacct_memory(charged);
        return error;
}

EXPORT_SYMBOL(do_mmap_pgoff);

/* Get an address range which is currently unmapped.
 * For shmat() with addr=0.
 *
 * Ugly calling convention alert:
 * Return value with the low bits set means error value,
 * ie
 *      if (ret & ~PAGE_MASK)
 *              error = ret;
 *
 * This function "knows" that -ENOMEM has the bits set.
 */
#ifndef HAVE_ARCH_UNMAPPED_AREA
static inline unsigned long
arch_get_unmapped_area(struct file *filp, unsigned long addr,
                unsigned long len, unsigned long pgoff, unsigned long flags, unsigned long exec)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long start_addr;

        if (len > TASK_SIZE)
                return -ENOMEM;

        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma(mm, addr);
                if (TASK_SIZE - len >= addr &&
                    (!vma || addr + len <= vma->vm_start))
                        return addr;
        }
        start_addr = addr = mm->free_area_cache;

full_search:
        for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
                /* At this point:  (!vma || addr < vma->vm_end). */
                if (TASK_SIZE - len < addr) {
                        /*
                         * Start a new search - just in case we missed
                         * some holes.
                         */
                        if (start_addr != TASK_UNMAPPED_BASE) {
                                start_addr = addr = TASK_UNMAPPED_BASE;
                                goto full_search;
                        }
                        return -ENOMEM;
                }
                if (!vma || addr + len <= vma->vm_start) {
                        /*
                         * Remember the place where we stopped the search:
                         */
                        mm->free_area_cache = addr + len;
                        return addr;
                }
                addr = vma->vm_end;
        }
}
#else
extern unsigned long
arch_get_unmapped_area(struct file *, unsigned long, unsigned long,
                        unsigned long, unsigned long, unsigned long);
#endif  

unsigned long
get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
                unsigned long pgoff, unsigned long flags, unsigned long exec)
{
        if (flags & MAP_FIXED) {
                unsigned long ret;

                if (addr > TASK_SIZE - len)
                        return -ENOMEM;
                if (addr & ~PAGE_MASK)
                        return -EINVAL;
                if (file && is_file_hugepages(file))  {
                        /*
                         * Check if the given range is hugepage aligned, and
                         * can be made suitable for hugepages.
                         */
                        ret = prepare_hugepage_range(addr, len);
                } else {
                        /*
                         * Ensure that a normal request is not falling in a
                         * reserved hugepage range.  For some archs like IA-64,
                         * there is a separate region for hugepages.
                         */
                        ret = is_hugepage_only_range(addr, len);
                }
                if (ret)
                        return -EINVAL;
                return addr;
        }

        if (file && file->f_op && file->f_op->get_unmapped_area)
                return file->f_op->get_unmapped_area(file, addr, len,
                                                pgoff, flags);

        return arch_get_unmapped_area(file, addr, len, pgoff, flags, exec);
}

EXPORT_SYMBOL(get_unmapped_area);

/* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long addr)
{
        struct vm_area_struct *vma = NULL;

        if (mm) {
                /* Check the cache first. */
                /* (Cache hit rate is typically around 35%.) */
                vma = mm->mmap_cache;
                if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
                        struct rb_node * rb_node;

                        rb_node = mm->mm_rb.rb_node;
                        vma = NULL;

                        while (rb_node) {
                                struct vm_area_struct * vma_tmp;

                                vma_tmp = rb_entry(rb_node,
                                                struct vm_area_struct, vm_rb);

                                if (vma_tmp->vm_end > addr) {
                                        vma = vma_tmp;
                                        if (vma_tmp->vm_start <= addr)
                                                break;
                                        rb_node = rb_node->rb_left;
                                } else
                                        rb_node = rb_node->rb_right;
                        }
                        if (vma)
                                mm->mmap_cache = vma;
                }
        }
        return vma;
}

EXPORT_SYMBOL(find_vma);

/* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
struct vm_area_struct *
find_vma_prev(struct mm_struct *mm, unsigned long addr,
                        struct vm_area_struct **pprev)
{
        struct vm_area_struct *vma = NULL, *prev = NULL;
        struct rb_node * rb_node;
        if (!mm)
                goto out;

        /* Guard against addr being lower than the first VMA */
        vma = mm->mmap;

        /* Go through the RB tree quickly. */
        rb_node = mm->mm_rb.rb_node;

        while (rb_node) {
                struct vm_area_struct *vma_tmp;
                vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);

                if (addr < vma_tmp->vm_end) {
                        rb_node = rb_node->rb_left;
                } else {
                        prev = vma_tmp;
                        if (!prev->vm_next || (addr < prev->vm_next->vm_end))
                                break;
                        rb_node = rb_node->rb_right;
                }
        }

out:
        *pprev = prev;
        return prev ? prev->vm_next : vma;
}


static int over_stack_limit(unsigned long sz)
{
        if (sz < EXEC_STACK_BIAS)
                return 0;
        return (sz - EXEC_STACK_BIAS) > current->rlim[RLIMIT_STACK].rlim_cur;
}

#ifdef CONFIG_STACK_GROWSUP
/*
 * vma is the first one with address > vma->vm_end.  Have to extend vma.
 */
int expand_stack(struct vm_area_struct * vma, unsigned long address)
{
        unsigned long grow;

        if (!(vma->vm_flags & VM_GROWSUP))
                return -EFAULT;

        /*
         * We must make sure the anon_vma is allocated
         * so that the anon_vma locking is not a noop.
         */
        if (unlikely(anon_vma_prepare(vma)))
                return -ENOMEM;
        anon_vma_lock(vma);

        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_sem in read mode.  We need the
         * anon_vma lock to serialize against concurrent expand_stacks.
         */
        address += 4 + PAGE_SIZE - 1;
        address &= PAGE_MASK;
        grow = (address - vma->vm_end) >> PAGE_SHIFT;

        /* Overcommit.. */
        if (security_vm_enough_memory(grow) ||
                !vx_vmpages_avail(vma->vm_mm, grow)) {
                anon_vma_unlock(vma);
                return -ENOMEM;
        }
        
        if (over_stack_limit(address - vma->vm_start) ||
                        ((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) >
                        current->rlim[RLIMIT_AS].rlim_cur) {
                anon_vma_unlock(vma);
                vm_unacct_memory(grow);
                return -ENOMEM;
        }

        vma->vm_end = address;
        // vma->vm_mm->total_vm += grow;
        vx_vmpages_add(vma->vm_mm, grow);
        if (vma->vm_flags & VM_LOCKED)
                // vma->vm_mm->locked_vm += grow;
                vx_vmlocked_add(vma->vm_mm, grow);
        anon_vma_unlock(vma);
        return 0;
}

struct vm_area_struct *
find_extend_vma(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma, *prev;

        addr &= PAGE_MASK;
        vma = find_vma_prev(mm, addr, &prev);
        if (vma && (vma->vm_start <= addr))
                return vma;
        if (!prev || expand_stack(prev, addr))
                return NULL;
        if (prev->vm_flags & VM_LOCKED) {
                make_pages_present(addr, prev->vm_end);
        }
        return prev;
}
#else
/*
 * vma is the first one with address < vma->vm_start.  Have to extend vma.
 */
int expand_stack(struct vm_area_struct *vma, unsigned long address)
{
        unsigned long grow;

        /*
         * We must make sure the anon_vma is allocated
         * so that the anon_vma locking is not a noop.
         */
        if (unlikely(anon_vma_prepare(vma)))
                return -ENOMEM;
        anon_vma_lock(vma);

        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_sem in read mode.  We need the
         * anon_vma lock to serialize against concurrent expand_stacks.
         */
        address &= PAGE_MASK;
        grow = (vma->vm_start - address) >> PAGE_SHIFT;

        /* Overcommit.. */
        if (security_vm_enough_memory(grow) ||
                !vx_vmpages_avail(vma->vm_mm, grow)) {
                anon_vma_unlock(vma);
                return -ENOMEM;
        }
        
        if (over_stack_limit(vma->vm_end - address) ||
                        ((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) >
                        current->rlim[RLIMIT_AS].rlim_cur) {
                anon_vma_unlock(vma);
                vm_unacct_memory(grow);
                return -ENOMEM;
        }

        vma->vm_start = address;
        vma->vm_pgoff -= grow;
        // vma->vm_mm->total_vm += grow;
        vx_vmpages_add(vma->vm_mm, grow);
        if (vma->vm_flags & VM_LOCKED)
                // vma->vm_mm->locked_vm += grow;
                vx_vmlocked_add(vma->vm_mm, grow);
        anon_vma_unlock(vma);
        return 0;
}

struct vm_area_struct *
find_extend_vma(struct mm_struct * mm, unsigned long addr)
{
        struct vm_area_struct * vma;
        unsigned long start;

        addr &= PAGE_MASK;
        vma = find_vma(mm,addr);
        if (!vma)
                return NULL;
        if (vma->vm_start <= addr)
                return vma;
        if (!(vma->vm_flags & VM_GROWSDOWN))
                return NULL;
        start = vma->vm_start;
        if (expand_stack(vma, addr))
                return NULL;
        if (vma->vm_flags & VM_LOCKED) {
                make_pages_present(addr, start);
        }
        return vma;
}
#endif

/*
 * Try to free as many page directory entries as we can,
 * without having to work very hard at actually scanning
 * the page tables themselves.
 *
 * Right now we try to free page tables if we have a nice
 * PGDIR-aligned area that got free'd up. We could be more
 * granular if we want to, but this is fast and simple,
 * and covers the bad cases.
 *
 * "prev", if it exists, points to a vma before the one
 * we just free'd - but there's no telling how much before.
 */
static void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *prev,
        unsigned long start, unsigned long end)
{
        unsigned long first = start & PGDIR_MASK;
        unsigned long last = end + PGDIR_SIZE - 1;
        unsigned long start_index, end_index;
        struct mm_struct *mm = tlb->mm;

        if (!prev) {
                prev = mm->mmap;
                if (!prev)
                        goto no_mmaps;
                if (prev->vm_end > start) {
                        if (last > prev->vm_start)
                                last = prev->vm_start;
                        goto no_mmaps;
                }
        }
        for (;;) {
                struct vm_area_struct *next = prev->vm_next;

                if (next) {
                        if (next->vm_start < start) {
                                prev = next;
                                continue;
                        }
                        if (last > next->vm_start)
                                last = next->vm_start;
                }
                if (prev->vm_end > first)
                        first = prev->vm_end + PGDIR_SIZE - 1;
                break;
        }
no_mmaps:
        if (last < first)       /* for arches with discontiguous pgd indices */
                return;
        /*
         * If the PGD bits are not consecutive in the virtual address, the
         * old method of shifting the VA >> by PGDIR_SHIFT doesn't work.
         */
        start_index = pgd_index(first);
        if (start_index < FIRST_USER_PGD_NR)
                start_index = FIRST_USER_PGD_NR;
        end_index = pgd_index(last);
        if (end_index > start_index) {
                clear_page_tables(tlb, start_index, end_index - start_index);
                flush_tlb_pgtables(mm, first & PGDIR_MASK, last & PGDIR_MASK);
        }
}

/* Normal function to fix up a mapping
 * This function is the default for when an area has no specific
 * function.  This may be used as part of a more specific routine.
 *
 * By the time this function is called, the area struct has been
 * removed from the process mapping list.
 */
static void unmap_vma(struct mm_struct *mm, struct vm_area_struct *area)
{
        size_t len = area->vm_end - area->vm_start;
        unsigned long old_end = area->vm_end;

        // area->vm_mm->total_vm -= len >> PAGE_SHIFT;
        vx_vmpages_sub(area->vm_mm, len >> PAGE_SHIFT);
        
        if (area->vm_flags & VM_LOCKED)
                // area->vm_mm->locked_vm -= len >> PAGE_SHIFT;
                vx_vmlocked_sub(area->vm_mm, len >> PAGE_SHIFT);
        /*
         * Is this a new hole at the lowest possible address?
         */
        if (area->vm_start >= TASK_UNMAPPED_BASE &&
                                area->vm_start < area->vm_mm->free_area_cache)
              area->vm_mm->free_area_cache = area->vm_start;
        /*
         * Is this a new hole at the highest possible address?
         */
        if (area->vm_start > area->vm_mm->non_executable_cache)
                area->vm_mm->non_executable_cache = area->vm_start;
        remove_vm_struct(area);
        if (unlikely(area->vm_flags & VM_EXEC))
                arch_remove_exec_range(mm, old_end);
}

/*
 * Update the VMA and inode share lists.
 *
 * Ok - we have the memory areas we should free on the 'free' list,
 * so release them, and do the vma updates.
 */
static void unmap_vma_list(struct mm_struct *mm,
        struct vm_area_struct *mpnt)
{
        do {
                struct vm_area_struct *next = mpnt->vm_next;
                unmap_vma(mm, mpnt);
                mpnt = next;
        } while (mpnt != NULL);
        validate_mm(mm);
}

/*
 * Get rid of page table information in the indicated region.
 *
 * Called with the page table lock held.
 */
static void unmap_region(struct mm_struct *mm,
        struct vm_area_struct *vma,
        struct vm_area_struct *prev,
        unsigned long start,
        unsigned long end)
{
        struct mmu_gather *tlb;
        unsigned long nr_accounted = 0;

        lru_add_drain();
        tlb = tlb_gather_mmu(mm, 0);
        unmap_vmas(&tlb, mm, vma, start, end, &nr_accounted, NULL);
        vm_unacct_memory(nr_accounted);

        if (is_hugepage_only_range(start, end - start))
                hugetlb_free_pgtables(tlb, prev, start, end);
        else
                free_pgtables(tlb, prev, start, end);
        tlb_finish_mmu(tlb, start, end);
}

/*
 * Create a list of vma's touched by the unmap, removing them from the mm's
 * vma list as we go..
 */
static void
detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
        struct vm_area_struct *prev, unsigned long end)
{
        struct vm_area_struct **insertion_point;
        struct vm_area_struct *tail_vma = NULL;

        insertion_point = (prev ? &prev->vm_next : &mm->mmap);
        do {
                rb_erase(&vma->vm_rb, &mm->mm_rb);
                mm->map_count--;
                tail_vma = vma;
                vma = vma->vm_next;
        } while (vma && vma->vm_start < end);
        *insertion_point = vma;
        tail_vma->vm_next = NULL;
        mm->mmap_cache = NULL;          /* Kill the cache. */
}

/*
 * Split a vma into two pieces at address 'addr', a new vma is allocated
 * either for the first part or the the tail.
 */
int split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
              unsigned long addr, int new_below)
{
        struct mempolicy *pol;
        struct vm_area_struct *new;

        if (mm->map_count >= sysctl_max_map_count)
                return -ENOMEM;

        new = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
        if (!new)
                return -ENOMEM;

        /* most fields are the same, copy all, and then fixup */
        *new = *vma;

        if (new_below)
                new->vm_end = addr;
        else {
                new->vm_start = addr;
                new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
        }

        pol = mpol_copy(vma_policy(vma));
        if (IS_ERR(pol)) {
                kmem_cache_free(vm_area_cachep, new);
                return PTR_ERR(pol);
        }
        vma_set_policy(new, pol);

        if (new->vm_file)
                get_file(new->vm_file);

        if (new->vm_ops && new->vm_ops->open)
                new->vm_ops->open(new);

        if (new_below) {
                unsigned long old_end = vma->vm_end;

                vma_adjust(vma, addr, vma->vm_end, vma->vm_pgoff +
                        ((addr - new->vm_start) >> PAGE_SHIFT), new);
                if (vma->vm_flags & VM_EXEC)
                        arch_remove_exec_range(mm, old_end);
        } else
                vma_adjust(vma, vma->vm_start, addr, vma->vm_pgoff, new);

        return 0;
}

/* Munmap is split into 2 main parts -- this part which finds
 * what needs doing, and the areas themselves, which do the
 * work.  This now handles partial unmappings.
 * Jeremy Fitzhardinge <jeremy@goop.org>
 */
int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
{
        unsigned long end;
        struct vm_area_struct *mpnt, *prev, *last;

        if ((start & ~PAGE_MASK) || start > TASK_SIZE || len > TASK_SIZE-start)
                return -EINVAL;

        if ((len = PAGE_ALIGN(len)) == 0)
                return -EINVAL;

        /* Find the first overlapping VMA */
        mpnt = find_vma_prev(mm, start, &prev);
        if (!mpnt)
                return 0;
        /* we have  start < mpnt->vm_end  */

        if (is_vm_hugetlb_page(mpnt)) {
                int ret = is_aligned_hugepage_range(start, len);

                if (ret)
                        return ret;
        }

        /* if it doesn't overlap, we have nothing.. */
        end = start + len;
        if (mpnt->vm_start >= end)
                return 0;

        /* Something will probably happen, so notify. */
        if (mpnt->vm_file && (mpnt->vm_flags & VM_EXEC))
                profile_exec_unmap(mm);
 
        /*
         * If we need to split any vma, do it now to save pain later.
         *
         * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
         * unmapped vm_area_struct will remain in use: so lower split_vma
         * places tmp vma above, and higher split_vma places tmp vma below.
         */
        if (start > mpnt->vm_start) {
                if (split_vma(mm, mpnt, start, 0))
                        return -ENOMEM;
                prev = mpnt;
        }

        /* Does it split the last one? */
        last = find_vma(mm, end);
        if (last && end > last->vm_start) {
                if (split_vma(mm, last, end, 1))
                        return -ENOMEM;
        }
        mpnt = prev? prev->vm_next: mm->mmap;

        /*
         * Remove the vma's, and unmap the actual pages
         */
        detach_vmas_to_be_unmapped(mm, mpnt, prev, end);
        spin_lock(&mm->page_table_lock);
        unmap_region(mm, mpnt, prev, start, end);
        spin_unlock(&mm->page_table_lock);

        /* Fix up all other VM information */
        unmap_vma_list(mm, mpnt);

        return 0;
}

EXPORT_SYMBOL(do_munmap);

asmlinkage long sys_munmap(unsigned long addr, size_t len)
{
        int ret;
        struct mm_struct *mm = current->mm;

        down_write(&mm->mmap_sem);
        ret = do_munmap(mm, addr, len);
        up_write(&mm->mmap_sem);
        return ret;
}

/*
 *  this is really a simplified "do_mmap".  it only handles
 *  anonymous maps.  eventually we may be able to do some
 *  brk-specific accounting here.
 */
unsigned long do_brk(unsigned long addr, unsigned long len)
{
        struct mm_struct * mm = current->mm;
        struct vm_area_struct * vma, * prev;
        unsigned long flags;
        struct rb_node ** rb_link, * rb_parent;
        pgoff_t pgoff = addr >> PAGE_SHIFT;

        len = PAGE_ALIGN(len);
        if (!len)
                return addr;

        if ((addr + len) > TASK_SIZE || (addr + len) < addr)
                return -EINVAL;

        /*
         * mlock MCL_FUTURE?
         */
        if (mm->def_flags & VM_LOCKED) {
                unsigned long locked, lock_limit;
                locked = mm->locked_vm << PAGE_SHIFT;
                lock_limit = current->rlim[RLIMIT_MEMLOCK].rlim_cur;
                locked += len;
                if (locked > lock_limit && !capable(CAP_IPC_LOCK))
                        return -EAGAIN;
                /* vserver checks ? */
        }

        /*
         * Clear old maps.  this also does some error checking for us
         */
 munmap_back:
        vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
        if (vma && vma->vm_start < addr + len) {
                if (do_munmap(mm, addr, len))
                        return -ENOMEM;
                goto munmap_back;
        }

        /* Check against address space limits *after* clearing old maps... */
        if ((mm->total_vm << PAGE_SHIFT) + len
            > current->rlim[RLIMIT_AS].rlim_cur)
                return -ENOMEM;

        if (mm->map_count > sysctl_max_map_count)
                return -ENOMEM;

        if (security_vm_enough_memory(len >> PAGE_SHIFT) ||
                !vx_vmpages_avail(mm, len >> PAGE_SHIFT))
                return -ENOMEM;

        flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;

        /* Can we just expand an old private anonymous mapping? */
        if (vma_merge(mm, prev, addr, addr + len, flags,
                                        NULL, NULL, pgoff, NULL))
                goto out;

        /*
         * create a vma struct for an anonymous mapping
         */
        vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
        if (!vma) {
                vm_unacct_memory(len >> PAGE_SHIFT);
                return -ENOMEM;
        }
        memset(vma, 0, sizeof(*vma));

        vma->vm_mm = mm;
        vma->vm_start = addr;
        vma->vm_end = addr + len;
        vma->vm_pgoff = pgoff;
        vma->vm_flags = flags;
        vma->vm_page_prot = protection_map[flags & 0x0f];
        vma_link(mm, vma, prev, rb_link, rb_parent);
out:
        // mm->total_vm += len >> PAGE_SHIFT;
        vx_vmpages_add(mm, len >> PAGE_SHIFT);
        if (flags & VM_LOCKED) {
                // mm->locked_vm += len >> PAGE_SHIFT;
                vx_vmlocked_add(mm, len >> PAGE_SHIFT);
                make_pages_present(addr, addr + len);
        }
        return addr;
}

EXPORT_SYMBOL(do_brk);

/* Release all mmaps. */
void exit_mmap(struct mm_struct *mm)
{
        struct mmu_gather *tlb;
        struct vm_area_struct *vma;
        unsigned long nr_accounted = 0;

        profile_exit_mmap(mm);
 
        lru_add_drain();

        spin_lock(&mm->page_table_lock);

        tlb = tlb_gather_mmu(mm, 1);
        flush_cache_mm(mm);
        /* Use ~0UL here to ensure all VMAs in the mm are unmapped */
        mm->map_count -= unmap_vmas(&tlb, mm, mm->mmap, 0,
                                        ~0UL, &nr_accounted, NULL);
        vm_unacct_memory(nr_accounted);
        BUG_ON(mm->map_count);  /* This is just debugging */
        clear_page_tables(tlb, FIRST_USER_PGD_NR, USER_PTRS_PER_PGD);
        tlb_finish_mmu(tlb, 0, MM_VM_SIZE(mm));

        vma = mm->mmap;
        mm->mmap = mm->mmap_cache = NULL;
        mm->mm_rb = RB_ROOT;
        // mm->rss = 0;
        vx_rsspages_sub(mm, mm->rss);
        // mm->total_vm = 0;
        vx_vmpages_sub(mm, mm->total_vm);
        // mm->locked_vm = 0;
        vx_vmlocked_sub(mm, mm->locked_vm);
        arch_flush_exec_range(mm);

        spin_unlock(&mm->page_table_lock);

        /*
         * Walk the list again, actually closing and freeing it
         * without holding any MM locks.
         */
        while (vma) {
                struct vm_area_struct *next = vma->vm_next;
                remove_vm_struct(vma);
                vma = next;
        }
}

/* Insert vm structure into process list sorted by address
 * and into the inode's i_mmap tree.  If vm_file is non-NULL
 * then i_mmap_lock is taken here.
 */
void insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
{
        struct vm_area_struct * __vma, * prev;
        struct rb_node ** rb_link, * rb_parent;

        /*
         * The vm_pgoff of a purely anonymous vma should be irrelevant
         * until its first write fault, when page's anon_vma and index
         * are set.  But now set the vm_pgoff it will almost certainly
         * end up with (unless mremap moves it elsewhere before that
         * first wfault), so /proc/pid/maps tells a consistent story.
         *
         * By setting it to reflect the virtual start address of the
         * vma, merges and splits can happen in a seamless way, just
         * using the existing file pgoff checks and manipulations.
         * Similarly in do_mmap_pgoff and in do_brk.
         */
        if (!vma->vm_file) {
                BUG_ON(vma->anon_vma);
                vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
        }
        __vma = find_vma_prepare(mm,vma->vm_start,&prev,&rb_link,&rb_parent);
        if (__vma && __vma->vm_start < vma->vm_end)
                BUG();
        vma_link(mm, vma, prev, rb_link, rb_parent);
}

/*
 * Copy the vma structure to a new location in the same mm,
 * prior to moving page table entries, to effect an mremap move.
 */
struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
        unsigned long addr, unsigned long len, pgoff_t pgoff)
{
        struct vm_area_struct *vma = *vmap;
        unsigned long vma_start = vma->vm_start;
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *new_vma, *prev;
        struct rb_node **rb_link, *rb_parent;
        struct mempolicy *pol;

        /*
         * If anonymous vma has not yet been faulted, update new pgoff
         * to match new location, to increase its chance of merging.
         */
        if (!vma->vm_file && !vma->anon_vma)
                pgoff = addr >> PAGE_SHIFT;

        find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
        new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
                        vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
        if (new_vma) {
                /*
                 * Source vma may have been merged into new_vma
                 */
                if (vma_start >= new_vma->vm_start &&
                    vma_start < new_vma->vm_end)
                        *vmap = new_vma;
        } else {
                new_vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
                if (new_vma) {
                        *new_vma = *vma;
                        pol = mpol_copy(vma_policy(vma));
                        if (IS_ERR(pol)) {
                                kmem_cache_free(vm_area_cachep, new_vma);
                                return NULL;
                        }
                        vma_set_policy(new_vma, pol);
                        new_vma->vm_start = addr;
                        new_vma->vm_end = addr + len;
                        new_vma->vm_pgoff = pgoff;
                        if (new_vma->vm_file)
                                get_file(new_vma->vm_file);
                        if (new_vma->vm_ops && new_vma->vm_ops->open)
                                new_vma->vm_ops->open(new_vma);
                        vma_link(mm, new_vma, prev, rb_link, rb_parent);
                }
        }
        return new_vma;
}