/* * linux/mm/vmscan.c * * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds * * Swap reorganised 29.12.95, Stephen Tweedie. * kswapd added: 7.1.96 sct * Removed kswapd_ctl limits, and swap out as many pages as needed * to bring the system back to freepages.high: 2.4.97, Rik van Riel. * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com). * Multiqueue VM started 5.8.00, Rik van Riel. */ #include #include #include #include #include #include #include #include #include #include #include #include #include /* for try_to_release_page(), buffer_heads_over_limit */ #include #include #include #include #include #include #include #include #include #include #include /* * From 0 .. 100. Higher means more swappy. */ int vm_swappiness = 60; static long total_memory; #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru)) #ifdef ARCH_HAS_PREFETCH #define prefetch_prev_lru_page(_page, _base, _field) \ do { \ if ((_page)->lru.prev != _base) { \ struct page *prev; \ \ prev = lru_to_page(&(_page->lru)); \ prefetch(&prev->_field); \ } \ } while (0) #else #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0) #endif #ifdef ARCH_HAS_PREFETCHW #define prefetchw_prev_lru_page(_page, _base, _field) \ do { \ if ((_page)->lru.prev != _base) { \ struct page *prev; \ \ prev = lru_to_page(&(_page->lru)); \ prefetchw(&prev->_field); \ } \ } while (0) #else #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0) #endif /* * The list of shrinker callbacks used by to apply pressure to * ageable caches. */ struct shrinker { shrinker_t shrinker; struct list_head list; int seeks; /* seeks to recreate an obj */ long nr; /* objs pending delete */ }; static LIST_HEAD(shrinker_list); static DECLARE_MUTEX(shrinker_sem); /* * Add a shrinker callback to be called from the vm */ struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker) { struct shrinker *shrinker; shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL); if (shrinker) { shrinker->shrinker = theshrinker; shrinker->seeks = seeks; shrinker->nr = 0; down(&shrinker_sem); list_add(&shrinker->list, &shrinker_list); up(&shrinker_sem); } return shrinker; } EXPORT_SYMBOL(set_shrinker); /* * Remove one */ void remove_shrinker(struct shrinker *shrinker) { down(&shrinker_sem); list_del(&shrinker->list); up(&shrinker_sem); kfree(shrinker); } EXPORT_SYMBOL(remove_shrinker); #define SHRINK_BATCH 128 /* * Call the shrink functions to age shrinkable caches * * Here we assume it costs one seek to replace a lru page and that it also * takes a seek to recreate a cache object. With this in mind we age equal * percentages of the lru and ageable caches. This should balance the seeks * generated by these structures. * * If the vm encounted mapped pages on the LRU it increase the pressure on * slab to avoid swapping. * * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits. */ static int shrink_slab(unsigned long scanned, unsigned int gfp_mask) { struct shrinker *shrinker; long pages; if (down_trylock(&shrinker_sem)) return 0; pages = nr_used_zone_pages(); list_for_each_entry(shrinker, &shrinker_list, list) { unsigned long long delta; delta = (4 * scanned) / shrinker->seeks; delta *= (*shrinker->shrinker)(0, gfp_mask); do_div(delta, pages + 1); shrinker->nr += delta; if (shrinker->nr < 0) shrinker->nr = LONG_MAX; /* It wrapped! */ if (shrinker->nr <= SHRINK_BATCH) continue; while (shrinker->nr) { long this_scan = shrinker->nr; int shrink_ret; if (this_scan > 128) this_scan = 128; shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask); mod_page_state(slabs_scanned, this_scan); shrinker->nr -= this_scan; if (shrink_ret == -1) break; cond_resched(); } } up(&shrinker_sem); return 0; } /* Must be called with page's rmap lock held. */ static inline int page_mapping_inuse(struct page *page) { struct address_space *mapping; /* Page is in somebody's page tables. */ if (page_mapped(page)) return 1; /* Be more reluctant to reclaim swapcache than pagecache */ if (PageSwapCache(page)) return 1; mapping = page_mapping(page); if (!mapping) return 0; /* File is mmap'd by somebody? */ return mapping_mapped(mapping); } static inline int is_page_cache_freeable(struct page *page) { return page_count(page) - !!PagePrivate(page) == 2; } static int may_write_to_queue(struct backing_dev_info *bdi) { if (current_is_kswapd()) return 1; if (current_is_pdflush()) /* This is unlikely, but why not... */ return 1; if (!bdi_write_congested(bdi)) return 1; if (bdi == current->backing_dev_info) return 1; return 0; } /* * We detected a synchronous write error writing a page out. Probably * -ENOSPC. We need to propagate that into the address_space for a subsequent * fsync(), msync() or close(). * * The tricky part is that after writepage we cannot touch the mapping: nothing * prevents it from being freed up. But we have a ref on the page and once * that page is locked, the mapping is pinned. * * We're allowed to run sleeping lock_page() here because we know the caller has * __GFP_FS. */ static void handle_write_error(struct address_space *mapping, struct page *page, int error) { lock_page(page); if (page_mapping(page) == mapping) { if (error == -ENOSPC) set_bit(AS_ENOSPC, &mapping->flags); else set_bit(AS_EIO, &mapping->flags); } unlock_page(page); } /* possible outcome of pageout() */ typedef enum { /* failed to write page out, page is locked */ PAGE_KEEP, /* move page to the active list, page is locked */ PAGE_ACTIVATE, /* page has been sent to the disk successfully, page is unlocked */ PAGE_SUCCESS, /* page is clean and locked */ PAGE_CLEAN, } pageout_t; /* * pageout is called by shrink_list() for each dirty page. Calls ->writepage(). */ static pageout_t pageout(struct page *page, struct address_space *mapping) { /* * If the page is dirty, only perform writeback if that write * will be non-blocking. To prevent this allocation from being * stalled by pagecache activity. But note that there may be * stalls if we need to run get_block(). We could test * PagePrivate for that. * * If this process is currently in generic_file_write() against * this page's queue, we can perform writeback even if that * will block. * * If the page is swapcache, write it back even if that would * block, for some throttling. This happens by accident, because * swap_backing_dev_info is bust: it doesn't reflect the * congestion state of the swapdevs. Easy to fix, if needed. * See swapfile.c:page_queue_congested(). */ if (!is_page_cache_freeable(page)) return PAGE_KEEP; if (!mapping) return PAGE_KEEP; if (mapping->a_ops->writepage == NULL) return PAGE_ACTIVATE; if (!may_write_to_queue(mapping->backing_dev_info)) return PAGE_KEEP; if (clear_page_dirty_for_io(page)) { int res; struct writeback_control wbc = { .sync_mode = WB_SYNC_NONE, .nr_to_write = SWAP_CLUSTER_MAX, .nonblocking = 1, .for_reclaim = 1, }; SetPageReclaim(page); res = mapping->a_ops->writepage(page, &wbc); if (res < 0) handle_write_error(mapping, page, res); if (res == WRITEPAGE_ACTIVATE) { ClearPageReclaim(page); return PAGE_ACTIVATE; } if (!PageWriteback(page)) { /* synchronous write or broken a_ops? */ ClearPageReclaim(page); } return PAGE_SUCCESS; } return PAGE_CLEAN; } struct scan_control { /* Ask refill_inactive_zone, or shrink_cache to scan this many pages */ unsigned long nr_to_scan; /* Incremented by the number of inactive pages that were scanned */ unsigned long nr_scanned; /* Incremented by the number of pages reclaimed */ unsigned long nr_reclaimed; unsigned long nr_mapped; /* From page_state */ /* Ask shrink_caches, or shrink_zone to scan at this priority */ unsigned int priority; /* This context's GFP mask */ unsigned int gfp_mask; int may_writepage; }; /* * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed */ static int shrink_list(struct list_head *page_list, struct scan_control *sc) { LIST_HEAD(ret_pages); struct pagevec freed_pvec; int pgactivate = 0; int reclaimed = 0; cond_resched(); pagevec_init(&freed_pvec, 1); while (!list_empty(page_list)) { struct address_space *mapping; struct page *page; int may_enter_fs; int referenced; page = lru_to_page(page_list); list_del(&page->lru); if (TestSetPageLocked(page)) goto keep; BUG_ON(PageActive(page)); if (PageWriteback(page)) goto keep_locked; sc->nr_scanned++; /* Double the slab pressure for mapped and swapcache pages */ if (page_mapped(page) || PageSwapCache(page)) sc->nr_scanned++; page_map_lock(page); referenced = page_referenced(page); if (referenced && page_mapping_inuse(page)) { /* In active use or really unfreeable. Activate it. */ page_map_unlock(page); goto activate_locked; } #ifdef CONFIG_SWAP /* * Anonymous process memory has backing store? * Try to allocate it some swap space here. * * XXX: implement swap clustering ? */ if (PageAnon(page) && !PageSwapCache(page)) { page_map_unlock(page); if (!add_to_swap(page)) goto activate_locked; page_map_lock(page); } #endif /* CONFIG_SWAP */ mapping = page_mapping(page); may_enter_fs = (sc->gfp_mask & __GFP_FS) || (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); /* * The page is mapped into the page tables of one or more * processes. Try to unmap it here. */ if (page_mapped(page) && mapping) { switch (try_to_unmap(page)) { case SWAP_FAIL: page_map_unlock(page); goto activate_locked; case SWAP_AGAIN: page_map_unlock(page); goto keep_locked; case SWAP_SUCCESS: ; /* try to free the page below */ } } page_map_unlock(page); if (PageDirty(page)) { if (referenced) goto keep_locked; if (!may_enter_fs) goto keep_locked; if (laptop_mode && !sc->may_writepage) goto keep_locked; /* Page is dirty, try to write it out here */ switch(pageout(page, mapping)) { case PAGE_KEEP: goto keep_locked; case PAGE_ACTIVATE: goto activate_locked; case PAGE_SUCCESS: if (PageWriteback(page) || PageDirty(page)) goto keep; /* * A synchronous write - probably a ramdisk. Go * ahead and try to reclaim the page. */ if (TestSetPageLocked(page)) goto keep; if (PageDirty(page) || PageWriteback(page)) goto keep_locked; mapping = page_mapping(page); case PAGE_CLEAN: ; /* try to free the page below */ } } /* * If the page has buffers, try to free the buffer mappings * associated with this page. If we succeed we try to free * the page as well. * * We do this even if the page is PageDirty(). * try_to_release_page() does not perform I/O, but it is * possible for a page to have PageDirty set, but it is actually * clean (all its buffers are clean). This happens if the * buffers were written out directly, with submit_bh(). ext3 * will do this, as well as the blockdev mapping. * try_to_release_page() will discover that cleanness and will * drop the buffers and mark the page clean - it can be freed. * * Rarely, pages can have buffers and no ->mapping. These are * the pages which were not successfully invalidated in * truncate_complete_page(). We try to drop those buffers here * and if that worked, and the page is no longer mapped into * process address space (page_count == 1) it can be freed. * Otherwise, leave the page on the LRU so it is swappable. */ if (PagePrivate(page)) { if (!try_to_release_page(page, sc->gfp_mask)) goto activate_locked; if (!mapping && page_count(page) == 1) goto free_it; } if (!mapping) goto keep_locked; /* truncate got there first */ spin_lock_irq(&mapping->tree_lock); /* * The non-racy check for busy page. It is critical to check * PageDirty _after_ making sure that the page is freeable and * not in use by anybody. (pagecache + us == 2) */ if (page_count(page) != 2 || PageDirty(page)) { spin_unlock_irq(&mapping->tree_lock); goto keep_locked; } #ifdef CONFIG_SWAP if (PageSwapCache(page)) { swp_entry_t swap = { .val = page->private }; __delete_from_swap_cache(page); spin_unlock_irq(&mapping->tree_lock); swap_free(swap); __put_page(page); /* The pagecache ref */ goto free_it; } #endif /* CONFIG_SWAP */ __remove_from_page_cache(page); spin_unlock_irq(&mapping->tree_lock); __put_page(page); free_it: unlock_page(page); reclaimed++; if (!pagevec_add(&freed_pvec, page)) __pagevec_release_nonlru(&freed_pvec); continue; activate_locked: SetPageActive(page); pgactivate++; keep_locked: unlock_page(page); keep: list_add(&page->lru, &ret_pages); BUG_ON(PageLRU(page)); } list_splice(&ret_pages, page_list); if (pagevec_count(&freed_pvec)) __pagevec_release_nonlru(&freed_pvec); mod_page_state(pgactivate, pgactivate); sc->nr_reclaimed += reclaimed; return reclaimed; } /* * zone->lru_lock is heavily contented. We relieve it by quickly privatising * a batch of pages and working on them outside the lock. Any pages which were * not freed will be added back to the LRU. * * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed * * For pagecache intensive workloads, the first loop here is the hottest spot * in the kernel (apart from the copy_*_user functions). */ static void shrink_cache(struct zone *zone, struct scan_control *sc) { LIST_HEAD(page_list); struct pagevec pvec; int max_scan = sc->nr_to_scan; pagevec_init(&pvec, 1); lru_add_drain(); spin_lock_irq(&zone->lru_lock); while (max_scan > 0) { struct page *page; int nr_taken = 0; int nr_scan = 0; int nr_freed; while (nr_scan++ < SWAP_CLUSTER_MAX && !list_empty(&zone->inactive_list)) { page = lru_to_page(&zone->inactive_list); prefetchw_prev_lru_page(page, &zone->inactive_list, flags); if (!TestClearPageLRU(page)) BUG(); list_del(&page->lru); if (get_page_testone(page)) { /* * It is being freed elsewhere */ __put_page(page); SetPageLRU(page); list_add(&page->lru, &zone->inactive_list); continue; } list_add(&page->lru, &page_list); nr_taken++; } zone->nr_inactive -= nr_taken; zone->pages_scanned += nr_taken; spin_unlock_irq(&zone->lru_lock); if (nr_taken == 0) goto done; max_scan -= nr_scan; if (current_is_kswapd()) mod_page_state_zone(zone, pgscan_kswapd, nr_scan); else mod_page_state_zone(zone, pgscan_direct, nr_scan); nr_freed = shrink_list(&page_list, sc); if (current_is_kswapd()) mod_page_state(kswapd_steal, nr_freed); mod_page_state_zone(zone, pgsteal, nr_freed); spin_lock_irq(&zone->lru_lock); /* * Put back any unfreeable pages. */ while (!list_empty(&page_list)) { page = lru_to_page(&page_list); if (TestSetPageLRU(page)) BUG(); list_del(&page->lru); if (PageActive(page)) add_page_to_active_list(zone, page); else add_page_to_inactive_list(zone, page); if (!pagevec_add(&pvec, page)) { spin_unlock_irq(&zone->lru_lock); __pagevec_release(&pvec); spin_lock_irq(&zone->lru_lock); } } } spin_unlock_irq(&zone->lru_lock); done: pagevec_release(&pvec); } /* * This moves pages from the active list to the inactive list. * * We move them the other way if the page is referenced by one or more * processes, from rmap. * * If the pages are mostly unmapped, the processing is fast and it is * appropriate to hold zone->lru_lock across the whole operation. But if * the pages are mapped, the processing is slow (page_referenced()) so we * should drop zone->lru_lock around each page. It's impossible to balance * this, so instead we remove the pages from the LRU while processing them. * It is safe to rely on PG_active against the non-LRU pages in here because * nobody will play with that bit on a non-LRU page. * * The downside is that we have to touch page->_count against each page. * But we had to alter page->flags anyway. */ static void refill_inactive_zone(struct zone *zone, struct scan_control *sc) { int pgmoved; int pgdeactivate = 0; int pgscanned = 0; int nr_pages = sc->nr_to_scan; LIST_HEAD(l_hold); /* The pages which were snipped off */ LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */ LIST_HEAD(l_active); /* Pages to go onto the active_list */ struct page *page; struct pagevec pvec; int reclaim_mapped = 0; long mapped_ratio; long distress; long swap_tendency; lru_add_drain(); pgmoved = 0; spin_lock_irq(&zone->lru_lock); while (pgscanned < nr_pages && !list_empty(&zone->active_list)) { page = lru_to_page(&zone->active_list); prefetchw_prev_lru_page(page, &zone->active_list, flags); if (!TestClearPageLRU(page)) BUG(); list_del(&page->lru); if (get_page_testone(page)) { /* * It was already free! release_pages() or put_page() * are about to remove it from the LRU and free it. So * put the refcount back and put the page back on the * LRU */ __put_page(page); SetPageLRU(page); list_add(&page->lru, &zone->active_list); } else { list_add(&page->lru, &l_hold); pgmoved++; } pgscanned++; } zone->nr_active -= pgmoved; spin_unlock_irq(&zone->lru_lock); /* * `distress' is a measure of how much trouble we're having reclaiming * pages. 0 -> no problems. 100 -> great trouble. */ distress = 100 >> zone->prev_priority; /* * The point of this algorithm is to decide when to start reclaiming * mapped memory instead of just pagecache. Work out how much memory * is mapped. */ mapped_ratio = (sc->nr_mapped * 100) / total_memory; /* * Now decide how much we really want to unmap some pages. The mapped * ratio is downgraded - just because there's a lot of mapped memory * doesn't necessarily mean that page reclaim isn't succeeding. * * The distress ratio is important - we don't want to start going oom. * * A 100% value of vm_swappiness overrides this algorithm altogether. */ swap_tendency = mapped_ratio / 2 + distress + vm_swappiness; /* * Now use this metric to decide whether to start moving mapped memory * onto the inactive list. */ if (swap_tendency >= 100) reclaim_mapped = 1; while (!list_empty(&l_hold)) { page = lru_to_page(&l_hold); list_del(&page->lru); if (page_mapped(page)) { if (!reclaim_mapped) { list_add(&page->lru, &l_active); continue; } page_map_lock(page); if (page_referenced(page)) { page_map_unlock(page); list_add(&page->lru, &l_active); continue; } page_map_unlock(page); } /* * FIXME: need to consider page_count(page) here if/when we * reap orphaned pages via the LRU (Daniel's locking stuff) */ if (total_swap_pages == 0 && PageAnon(page)) { list_add(&page->lru, &l_active); continue; } list_add(&page->lru, &l_inactive); } pagevec_init(&pvec, 1); pgmoved = 0; spin_lock_irq(&zone->lru_lock); while (!list_empty(&l_inactive)) { page = lru_to_page(&l_inactive); prefetchw_prev_lru_page(page, &l_inactive, flags); if (TestSetPageLRU(page)) BUG(); if (!TestClearPageActive(page)) BUG(); list_move(&page->lru, &zone->inactive_list); pgmoved++; if (!pagevec_add(&pvec, page)) { zone->nr_inactive += pgmoved; spin_unlock_irq(&zone->lru_lock); pgdeactivate += pgmoved; pgmoved = 0; if (buffer_heads_over_limit) pagevec_strip(&pvec); __pagevec_release(&pvec); spin_lock_irq(&zone->lru_lock); } } zone->nr_inactive += pgmoved; pgdeactivate += pgmoved; if (buffer_heads_over_limit) { spin_unlock_irq(&zone->lru_lock); pagevec_strip(&pvec); spin_lock_irq(&zone->lru_lock); } pgmoved = 0; while (!list_empty(&l_active)) { page = lru_to_page(&l_active); prefetchw_prev_lru_page(page, &l_active, flags); if (TestSetPageLRU(page)) BUG(); BUG_ON(!PageActive(page)); list_move(&page->lru, &zone->active_list); pgmoved++; if (!pagevec_add(&pvec, page)) { zone->nr_active += pgmoved; pgmoved = 0; spin_unlock_irq(&zone->lru_lock); __pagevec_release(&pvec); spin_lock_irq(&zone->lru_lock); } } zone->nr_active += pgmoved; spin_unlock_irq(&zone->lru_lock); pagevec_release(&pvec); mod_page_state_zone(zone, pgrefill, pgscanned); mod_page_state(pgdeactivate, pgdeactivate); } /* * Scan `nr_pages' from this zone. Returns the number of reclaimed pages. * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. */ static void shrink_zone(struct zone *zone, struct scan_control *sc) { unsigned long scan_active, scan_inactive; int count; scan_inactive = (zone->nr_active + zone->nr_inactive) >> sc->priority; /* * Try to keep the active list 2/3 of the size of the cache. And * make sure that refill_inactive is given a decent number of pages. * * The "scan_active + 1" here is important. With pagecache-intensive * workloads the inactive list is huge, and `ratio' evaluates to zero * all the time. Which pins the active list memory. So we add one to * `scan_active' just to make sure that the kernel will slowly sift * through the active list. */ if (zone->nr_active >= 4*(zone->nr_inactive*2 + 1)) { /* Don't scan more than 4 times the inactive list scan size */ scan_active = 4*scan_inactive; } else { unsigned long long tmp; /* Cast to long long so the multiply doesn't overflow */ tmp = (unsigned long long)scan_inactive * zone->nr_active; do_div(tmp, zone->nr_inactive*2 + 1); scan_active = (unsigned long)tmp; } atomic_add(scan_active + 1, &zone->nr_scan_active); count = atomic_read(&zone->nr_scan_active); if (count >= SWAP_CLUSTER_MAX) { atomic_set(&zone->nr_scan_active, 0); sc->nr_to_scan = count; refill_inactive_zone(zone, sc); } atomic_add(scan_inactive, &zone->nr_scan_inactive); count = atomic_read(&zone->nr_scan_inactive); if (count >= SWAP_CLUSTER_MAX) { atomic_set(&zone->nr_scan_inactive, 0); sc->nr_to_scan = count; shrink_cache(zone, sc); } } /* * This is the direct reclaim path, for page-allocating processes. We only * try to reclaim pages from zones which will satisfy the caller's allocation * request. * * We reclaim from a zone even if that zone is over pages_high. Because: * a) The caller may be trying to free *extra* pages to satisfy a higher-order * allocation or * b) The zones may be over pages_high but they must go *over* pages_high to * satisfy the `incremental min' zone defense algorithm. * * Returns the number of reclaimed pages. * * If a zone is deemed to be full of pinned pages then just give it a light * scan then give up on it. */ static void shrink_caches(struct zone **zones, struct scan_control *sc) { int i; for (i = 0; zones[i] != NULL; i++) { struct zone *zone = zones[i]; zone->temp_priority = sc->priority; if (zone->prev_priority > sc->priority) zone->prev_priority = sc->priority; if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY) continue; /* Let kswapd poll it */ shrink_zone(zone, sc); } } /* * This is the main entry point to direct page reclaim. * * If a full scan of the inactive list fails to free enough memory then we * are "out of memory" and something needs to be killed. * * If the caller is !__GFP_FS then the probability of a failure is reasonably * high - the zone may be full of dirty or under-writeback pages, which this * caller can't do much about. We kick pdflush and take explicit naps in the * hope that some of these pages can be written. But if the allocating task * holds filesystem locks which prevent writeout this might not work, and the * allocation attempt will fail. */ int try_to_free_pages(struct zone **zones, unsigned int gfp_mask, unsigned int order) { int priority; int ret = 0; int total_scanned = 0, total_reclaimed = 0; struct reclaim_state *reclaim_state = current->reclaim_state; struct scan_control sc; int i; sc.gfp_mask = gfp_mask; sc.may_writepage = 0; inc_page_state(allocstall); for (i = 0; zones[i] != 0; i++) zones[i]->temp_priority = DEF_PRIORITY; for (priority = DEF_PRIORITY; priority >= 0; priority--) { sc.nr_mapped = read_page_state(nr_mapped); sc.nr_scanned = 0; sc.nr_reclaimed = 0; sc.priority = priority; shrink_caches(zones, &sc); shrink_slab(sc.nr_scanned, gfp_mask); if (reclaim_state) { sc.nr_reclaimed += reclaim_state->reclaimed_slab; reclaim_state->reclaimed_slab = 0; } if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) { ret = 1; goto out; } total_scanned += sc.nr_scanned; total_reclaimed += sc.nr_reclaimed; /* * Try to write back as many pages as we just scanned. This * tends to cause slow streaming writers to write data to the * disk smoothly, at the dirtying rate, which is nice. But * that's undesirable in laptop mode, where we *want* lumpy * writeout. So in laptop mode, write out the whole world. */ if (total_scanned > SWAP_CLUSTER_MAX + SWAP_CLUSTER_MAX/2) { wakeup_bdflush(laptop_mode ? 0 : total_scanned); sc.may_writepage = 1; } /* Take a nap, wait for some writeback to complete */ if (sc.nr_scanned && priority < DEF_PRIORITY - 2) blk_congestion_wait(WRITE, HZ/10); } if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) out_of_memory(); out: for (i = 0; zones[i] != 0; i++) zones[i]->prev_priority = zones[i]->temp_priority; return ret; } /* * For kswapd, balance_pgdat() will work across all this node's zones until * they are all at pages_high. * * If `nr_pages' is non-zero then it is the number of pages which are to be * reclaimed, regardless of the zone occupancies. This is a software suspend * special. * * Returns the number of pages which were actually freed. * * There is special handling here for zones which are full of pinned pages. * This can happen if the pages are all mlocked, or if they are all used by * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. * What we do is to detect the case where all pages in the zone have been * scanned twice and there has been zero successful reclaim. Mark the zone as * dead and from now on, only perform a short scan. Basically we're polling * the zone for when the problem goes away. * * kswapd scans the zones in the highmem->normal->dma direction. It skips * zones which have free_pages > pages_high, but once a zone is found to have * free_pages <= pages_high, we scan that zone and the lower zones regardless * of the number of free pages in the lower zones. This interoperates with * the page allocator fallback scheme to ensure that aging of pages is balanced * across the zones. */ static int balance_pgdat(pg_data_t *pgdat, int nr_pages) { int to_free = nr_pages; int priority; int i; int total_scanned = 0, total_reclaimed = 0; struct reclaim_state *reclaim_state = current->reclaim_state; struct scan_control sc; sc.gfp_mask = GFP_KERNEL; sc.may_writepage = 0; sc.nr_mapped = read_page_state(nr_mapped); inc_page_state(pageoutrun); for (i = 0; i < pgdat->nr_zones; i++) { struct zone *zone = pgdat->node_zones + i; zone->temp_priority = DEF_PRIORITY; } for (priority = DEF_PRIORITY; priority >= 0; priority--) { int all_zones_ok = 1; int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ if (nr_pages == 0) { /* * Scan in the highmem->dma direction for the highest * zone which needs scanning */ for (i = pgdat->nr_zones - 1; i >= 0; i--) { struct zone *zone = pgdat->node_zones + i; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; if (zone->free_pages <= zone->pages_high) { end_zone = i; goto scan; } } goto out; } else { end_zone = pgdat->nr_zones - 1; } scan: /* * Now scan the zone in the dma->highmem direction, stopping * at the last zone which needs scanning. * * We do this because the page allocator works in the opposite * direction. This prevents the page allocator from allocating * pages behind kswapd's direction of progress, which would * cause too much scanning of the lower zones. */ for (i = 0; i <= end_zone; i++) { struct zone *zone = pgdat->node_zones + i; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; if (nr_pages == 0) { /* Not software suspend */ if (zone->free_pages <= zone->pages_high) all_zones_ok = 0; } zone->temp_priority = priority; if (zone->prev_priority > priority) zone->prev_priority = priority; sc.nr_scanned = 0; sc.nr_reclaimed = 0; sc.priority = priority; shrink_zone(zone, &sc); reclaim_state->reclaimed_slab = 0; shrink_slab(sc.nr_scanned, GFP_KERNEL); sc.nr_reclaimed += reclaim_state->reclaimed_slab; total_reclaimed += sc.nr_reclaimed; if (zone->all_unreclaimable) continue; if (zone->pages_scanned > zone->present_pages * 2) zone->all_unreclaimable = 1; /* * If we've done a decent amount of scanning and * the reclaim ratio is low, start doing writepage * even in laptop mode */ if (total_scanned > SWAP_CLUSTER_MAX * 2 && total_scanned > total_reclaimed+total_reclaimed/2) sc.may_writepage = 1; } if (nr_pages && to_free > total_reclaimed) continue; /* swsusp: need to do more work */ if (all_zones_ok) break; /* kswapd: all done */ /* * OK, kswapd is getting into trouble. Take a nap, then take * another pass across the zones. */ if (total_scanned && priority < DEF_PRIORITY - 2) blk_congestion_wait(WRITE, HZ/10); } out: for (i = 0; i < pgdat->nr_zones; i++) { struct zone *zone = pgdat->node_zones + i; zone->prev_priority = zone->temp_priority; } return total_reclaimed; } /* * The background pageout daemon, started as a kernel thread * from the init process. * * This basically trickles out pages so that we have _some_ * free memory available even if there is no other activity * that frees anything up. This is needed for things like routing * etc, where we otherwise might have all activity going on in * asynchronous contexts that cannot page things out. * * If there are applications that are active memory-allocators * (most normal use), this basically shouldn't matter. */ int kswapd(void *p) { pg_data_t *pgdat = (pg_data_t*)p; struct task_struct *tsk = current; DEFINE_WAIT(wait); struct reclaim_state reclaim_state = { .reclaimed_slab = 0, }; cpumask_t cpumask; daemonize("kswapd%d", pgdat->node_id); cpumask = node_to_cpumask(pgdat->node_id); if (!cpus_empty(cpumask)) set_cpus_allowed(tsk, cpumask); current->reclaim_state = &reclaim_state; /* * Tell the memory management that we're a "memory allocator", * and that if we need more memory we should get access to it * regardless (see "__alloc_pages()"). "kswapd" should * never get caught in the normal page freeing logic. * * (Kswapd normally doesn't need memory anyway, but sometimes * you need a small amount of memory in order to be able to * page out something else, and this flag essentially protects * us from recursively trying to free more memory as we're * trying to free the first piece of memory in the first place). */ tsk->flags |= PF_MEMALLOC|PF_KSWAPD; for ( ; ; ) { if (current->flags & PF_FREEZE) refrigerator(PF_FREEZE); prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); schedule(); finish_wait(&pgdat->kswapd_wait, &wait); balance_pgdat(pgdat, 0); } } /* * A zone is low on free memory, so wake its kswapd task to service it. */ void wakeup_kswapd(struct zone *zone) { if (zone->free_pages > zone->pages_low) return; if (!waitqueue_active(&zone->zone_pgdat->kswapd_wait)) return; wake_up_interruptible(&zone->zone_pgdat->kswapd_wait); } #ifdef CONFIG_PM /* * Try to free `nr_pages' of memory, system-wide. Returns the number of freed * pages. */ int shrink_all_memory(int nr_pages) { pg_data_t *pgdat; int nr_to_free = nr_pages; int ret = 0; struct reclaim_state reclaim_state = { .reclaimed_slab = 0, }; current->reclaim_state = &reclaim_state; for_each_pgdat(pgdat) { int freed; freed = balance_pgdat(pgdat, nr_to_free); ret += freed; nr_to_free -= freed; if (nr_to_free <= 0) break; } current->reclaim_state = NULL; return ret; } #endif #ifdef CONFIG_HOTPLUG_CPU /* It's optimal to keep kswapds on the same CPUs as their memory, but not required for correctness. So if the last cpu in a node goes away, we get changed to run anywhere: as the first one comes back, restore their cpu bindings. */ static int __devinit cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) { pg_data_t *pgdat; cpumask_t mask; if (action == CPU_ONLINE) { for_each_pgdat(pgdat) { mask = node_to_cpumask(pgdat->node_id); if (any_online_cpu(mask) != NR_CPUS) /* One of our CPUs online: restore mask */ set_cpus_allowed(pgdat->kswapd, mask); } } return NOTIFY_OK; } #endif /* CONFIG_HOTPLUG_CPU */ static int __init kswapd_init(void) { pg_data_t *pgdat; swap_setup(); for_each_pgdat(pgdat) pgdat->kswapd = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL)); total_memory = nr_free_pagecache_pages(); hotcpu_notifier(cpu_callback, 0); return 0; } module_init(kswapd_init)