/* * 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 <linux/mm.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/kernel_stat.h> #include <linux/swap.h> #include <linux/pagemap.h> #include <linux/init.h> #include <linux/highmem.h> #include <linux/file.h> #include <linux/writeback.h> #include <linux/blkdev.h> #include <linux/buffer_head.h> /* for try_to_release_page(), buffer_heads_over_limit */ #include <linux/mm_inline.h> #include <linux/pagevec.h> #include <linux/backing-dev.h> #include <linux/rmap.h> #include <linux/topology.h> #include <linux/cpu.h> #include <linux/cpuset.h> #include <linux/notifier.h> #include <linux/rwsem.h> #include <linux/delay.h> #include <asm/tlbflush.h> #include <asm/div64.h> #include <linux/swapops.h> #include "internal.h" struct scan_control { /* Incremented by the number of inactive pages that were scanned */ unsigned long nr_scanned; unsigned long nr_mapped; /* From page_state */ /* This context's GFP mask */ gfp_t gfp_mask; int may_writepage; /* Can pages be swapped as part of reclaim? */ int may_swap; /* This context's SWAP_CLUSTER_MAX. If freeing memory for * suspend, we effectively ignore SWAP_CLUSTER_MAX. * In this context, it doesn't matter that we scan the * whole list at once. */ int swap_cluster_max; }; /* * 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 */ }; #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 /* * From 0 .. 100. Higher means more swappy. */ int vm_swappiness = 60; static long total_memory; static LIST_HEAD(shrinker_list); static DECLARE_RWSEM(shrinker_rwsem); /* * 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_write(&shrinker_rwsem); list_add_tail(&shrinker->list, &shrinker_list); up_write(&shrinker_rwsem); } return shrinker; } EXPORT_SYMBOL(set_shrinker); /* * Remove one */ void remove_shrinker(struct shrinker *shrinker) { down_write(&shrinker_rwsem); list_del(&shrinker->list); up_write(&shrinker_rwsem); 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. * * `lru_pages' represents the number of on-LRU pages in all the zones which * are eligible for the caller's allocation attempt. It is used for balancing * slab reclaim versus page reclaim. * * Returns the number of slab objects which we shrunk. */ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask, unsigned long lru_pages) { struct shrinker *shrinker; unsigned long ret = 0; if (scanned == 0) scanned = SWAP_CLUSTER_MAX; if (!down_read_trylock(&shrinker_rwsem)) return 1; /* Assume we'll be able to shrink next time */ list_for_each_entry(shrinker, &shrinker_list, list) { unsigned long long delta; unsigned long total_scan; unsigned long max_pass = (*shrinker->shrinker)(0, gfp_mask); delta = (4 * scanned) / shrinker->seeks; delta *= max_pass; do_div(delta, lru_pages + 1); shrinker->nr += delta; if (shrinker->nr < 0) { printk(KERN_ERR "%s: nr=%ld\n", __FUNCTION__, shrinker->nr); shrinker->nr = max_pass; } /* * Avoid risking looping forever due to too large nr value: * never try to free more than twice the estimate number of * freeable entries. */ if (shrinker->nr > max_pass * 2) shrinker->nr = max_pass * 2; total_scan = shrinker->nr; shrinker->nr = 0; while (total_scan >= SHRINK_BATCH) { long this_scan = SHRINK_BATCH; int shrink_ret; int nr_before; nr_before = (*shrinker->shrinker)(0, gfp_mask); shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask); if (shrink_ret == -1) break; if (shrink_ret < nr_before) ret += nr_before - shrink_ret; mod_page_state(slabs_scanned, this_scan); total_scan -= this_scan; cond_resched(); } shrinker->nr += total_scan; } up_read(&shrinker_rwsem); return ret; } /* Called without lock on whether page is mapped, so answer is unstable */ 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->flags & PF_SWAPWRITE) 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); } /* * pageout is called by shrink_page_list() for each dirty page. * Calls ->writepage(). */ 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) { /* * Some data journaling orphaned pages can have * page->mapping == NULL while being dirty with clean buffers. */ if (PagePrivate(page)) { if (try_to_free_buffers(page)) { ClearPageDirty(page); printk("%s: orphaned page\n", __FUNCTION__); return PAGE_CLEAN; } } 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 == AOP_WRITEPAGE_ACTIVATE) { ClearPageReclaim(page); return PAGE_ACTIVATE; } if (!PageWriteback(page)) { /* synchronous write or broken a_ops? */ ClearPageReclaim(page); } return PAGE_SUCCESS; } return PAGE_CLEAN; } int remove_mapping(struct address_space *mapping, struct page *page) { if (!mapping) return 0; /* truncate got there first */ write_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 (unlikely(page_count(page) != 2)) goto cannot_free; smp_rmb(); if (unlikely(PageDirty(page))) goto cannot_free; if (PageSwapCache(page)) { swp_entry_t swap = { .val = page_private(page) }; __delete_from_swap_cache(page); write_unlock_irq(&mapping->tree_lock); swap_free(swap); __put_page(page); /* The pagecache ref */ return 1; } __remove_from_page_cache(page); write_unlock_irq(&mapping->tree_lock); __put_page(page); return 1; cannot_free: write_unlock_irq(&mapping->tree_lock); return 0; } /* * shrink_page_list() returns the number of reclaimed pages */ static unsigned long shrink_page_list(struct list_head *page_list, struct scan_control *sc) { LIST_HEAD(ret_pages); struct pagevec freed_pvec; int pgactivate = 0; unsigned long nr_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; cond_resched(); page = lru_to_page(page_list); list_del(&page->lru); if (TestSetPageLocked(page)) goto keep; BUG_ON(PageActive(page)); sc->nr_scanned++; if (!sc->may_swap && page_mapped(page)) goto keep_locked; /* Double the slab pressure for mapped and swapcache pages */ if (page_mapped(page) || PageSwapCache(page)) sc->nr_scanned++; if (PageWriteback(page)) goto keep_locked; referenced = page_referenced(page, 1); /* In active use or really unfreeable? Activate it. */ if (referenced && page_mapping_inuse(page)) goto activate_locked; #ifdef CONFIG_SWAP /* * Anonymous process memory has backing store? * Try to allocate it some swap space here. */ if (PageAnon(page) && !PageSwapCache(page)) if (!add_to_swap(page, GFP_ATOMIC)) goto activate_locked; #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, 0)) { case SWAP_FAIL: goto activate_locked; case SWAP_AGAIN: goto keep_locked; case SWAP_SUCCESS: ; /* try to free the page below */ } } if (PageDirty(page)) { if (referenced) goto keep_locked; if (!may_enter_fs) goto keep_locked; if (!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 (!remove_mapping(mapping, page)) goto keep_locked; free_it: unlock_page(page); nr_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); return nr_reclaimed; } /* * zone->lru_lock is heavily contended. Some of the functions that * shrink the lists perform better by taking out a batch of pages * and working on them outside the LRU lock. * * For pagecache intensive workloads, this function is the hottest * spot in the kernel (apart from copy_*_user functions). * * Appropriate locks must be held before calling this function. * * @nr_to_scan: The number of pages to look through on the list. * @src: The LRU list to pull pages off. * @dst: The temp list to put pages on to. * @scanned: The number of pages that were scanned. * * returns how many pages were moved onto *@dst. */ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, struct list_head *src, struct list_head *dst, unsigned long *scanned) { unsigned long nr_taken = 0; struct page *page; unsigned long scan; for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { struct list_head *target; page = lru_to_page(src); prefetchw_prev_lru_page(page, src, flags); BUG_ON(!PageLRU(page)); list_del(&page->lru); target = src; if (likely(get_page_unless_zero(page))) { /* * Be careful not to clear PageLRU until after we're * sure the page is not being freed elsewhere -- the * page release code relies on it. */ ClearPageLRU(page); target = dst; nr_taken++; } /* else it is being freed elsewhere */ list_add(&page->lru, target); } *scanned = scan; return nr_taken; } /* * shrink_inactive_list() is a helper for shrink_zone(). It returns the number * of reclaimed pages */ static unsigned long shrink_inactive_list(unsigned long max_scan, struct zone *zone, struct scan_control *sc) { LIST_HEAD(page_list); struct pagevec pvec; unsigned long nr_scanned = 0; unsigned long nr_reclaimed = 0; pagevec_init(&pvec, 1); lru_add_drain(); spin_lock_irq(&zone->lru_lock); do { struct page *page; unsigned long nr_taken; unsigned long nr_scan; unsigned long nr_freed; nr_taken = isolate_lru_pages(sc->swap_cluster_max, &zone->inactive_list, &page_list, &nr_scan); zone->nr_inactive -= nr_taken; zone->pages_scanned += nr_scan; spin_unlock_irq(&zone->lru_lock); nr_scanned += nr_scan; nr_freed = shrink_page_list(&page_list, sc); nr_reclaimed += nr_freed; local_irq_disable(); if (current_is_kswapd()) { __mod_page_state_zone(zone, pgscan_kswapd, nr_scan); __mod_page_state(kswapd_steal, nr_freed); } else __mod_page_state_zone(zone, pgscan_direct, nr_scan); __mod_page_state_zone(zone, pgsteal, nr_freed); if (nr_taken == 0) goto done; spin_lock(&zone->lru_lock); /* * Put back any unfreeable pages. */ while (!list_empty(&page_list)) { page = lru_to_page(&page_list); BUG_ON(PageLRU(page)); SetPageLRU(page); 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); } } } while (nr_scanned < max_scan); spin_unlock(&zone->lru_lock); done: local_irq_enable(); pagevec_release(&pvec); return nr_reclaimed; } /* * 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 shrink_active_list(unsigned long nr_pages, struct zone *zone, struct scan_control *sc) { unsigned long pgmoved; int pgdeactivate = 0; unsigned long pgscanned; 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; if (sc->may_swap) { long mapped_ratio; long distress; long swap_tendency; /* * `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; } lru_add_drain(); spin_lock_irq(&zone->lru_lock); pgmoved = isolate_lru_pages(nr_pages, &zone->active_list, &l_hold, &pgscanned); zone->pages_scanned += pgscanned; zone->nr_active -= pgmoved; spin_unlock_irq(&zone->lru_lock); while (!list_empty(&l_hold)) { cond_resched(); page = lru_to_page(&l_hold); list_del(&page->lru); if (page_mapped(page)) { if (!reclaim_mapped || (total_swap_pages == 0 && PageAnon(page)) || page_referenced(page, 0)) { 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); BUG_ON(PageLRU(page)); SetPageLRU(page); BUG_ON(!PageActive(page)); ClearPageActive(page); 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); BUG_ON(PageLRU(page)); SetPageLRU(page); 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(&zone->lru_lock); __mod_page_state_zone(zone, pgrefill, pgscanned); __mod_page_state(pgdeactivate, pgdeactivate); local_irq_enable(); pagevec_release(&pvec); } /* * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. */ static unsigned long shrink_zone(int priority, struct zone *zone, struct scan_control *sc) { unsigned long nr_active; unsigned long nr_inactive; unsigned long nr_to_scan; unsigned long nr_reclaimed = 0; atomic_inc(&zone->reclaim_in_progress); /* * Add one to `nr_to_scan' just to make sure that the kernel will * slowly sift through the active list. */ zone->nr_scan_active += (zone->nr_active >> priority) + 1; nr_active = zone->nr_scan_active; if (nr_active >= sc->swap_cluster_max) zone->nr_scan_active = 0; else nr_active = 0; zone->nr_scan_inactive += (zone->nr_inactive >> priority) + 1; nr_inactive = zone->nr_scan_inactive; if (nr_inactive >= sc->swap_cluster_max) zone->nr_scan_inactive = 0; else nr_inactive = 0; while (nr_active || nr_inactive) { if (nr_active) { nr_to_scan = min(nr_active, (unsigned long)sc->swap_cluster_max); nr_active -= nr_to_scan; shrink_active_list(nr_to_scan, zone, sc); } if (nr_inactive) { nr_to_scan = min(nr_inactive, (unsigned long)sc->swap_cluster_max); nr_inactive -= nr_to_scan; nr_reclaimed += shrink_inactive_list(nr_to_scan, zone, sc); } } throttle_vm_writeout(); atomic_dec(&zone->reclaim_in_progress); return nr_reclaimed; } /* * 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 unsigned long shrink_zones(int priority, struct zone **zones, struct scan_control *sc) { unsigned long nr_reclaimed = 0; int i; for (i = 0; zones[i] != NULL; i++) { struct zone *zone = zones[i]; if (!populated_zone(zone)) continue; if (!cpuset_zone_allowed(zone, __GFP_HARDWALL)) continue; zone->temp_priority = priority; if (zone->prev_priority > priority) zone->prev_priority = priority; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; /* Let kswapd poll it */ nr_reclaimed += shrink_zone(priority, zone, sc); } return nr_reclaimed; } /* * 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. */ unsigned long try_to_free_pages(struct zone **zones, gfp_t gfp_mask) { int priority; int ret = 0; unsigned long total_scanned = 0; unsigned long nr_reclaimed = 0; struct reclaim_state *reclaim_state = current->reclaim_state; unsigned long lru_pages = 0; int i; struct scan_control sc = { .gfp_mask = gfp_mask, .may_writepage = !laptop_mode, .swap_cluster_max = SWAP_CLUSTER_MAX, .may_swap = 1, }; inc_page_state(allocstall); for (i = 0; zones[i] != NULL; i++) { struct zone *zone = zones[i]; if (!cpuset_zone_allowed(zone, __GFP_HARDWALL)) continue; zone->temp_priority = DEF_PRIORITY; lru_pages += zone->nr_active + zone->nr_inactive; } for (priority = DEF_PRIORITY; priority >= 0; priority--) { sc.nr_mapped = read_page_state(nr_mapped); sc.nr_scanned = 0; if (!priority) disable_swap_token(); nr_reclaimed += shrink_zones(priority, zones, &sc); shrink_slab(sc.nr_scanned, gfp_mask, lru_pages); if (reclaim_state) { nr_reclaimed += reclaim_state->reclaimed_slab; reclaim_state->reclaimed_slab = 0; } total_scanned += sc.nr_scanned; if (nr_reclaimed >= sc.swap_cluster_max) { ret = 1; goto out; } /* * 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 > sc.swap_cluster_max + sc.swap_cluster_max / 2) { wakeup_pdflush(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); } out: for (i = 0; zones[i] != 0; i++) { struct zone *zone = zones[i]; if (!cpuset_zone_allowed(zone, __GFP_HARDWALL)) continue; zone->prev_priority = zone->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 unsigned long balance_pgdat(pg_data_t *pgdat, unsigned long nr_pages, int order) { unsigned long to_free = nr_pages; int all_zones_ok; int priority; int i; unsigned long total_scanned; unsigned long nr_reclaimed; struct reclaim_state *reclaim_state = current->reclaim_state; struct scan_control sc = { .gfp_mask = GFP_KERNEL, .may_swap = 1, .swap_cluster_max = nr_pages ? nr_pages : SWAP_CLUSTER_MAX, }; loop_again: total_scanned = 0; nr_reclaimed = 0; sc.may_writepage = !laptop_mode; 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 end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ unsigned long lru_pages = 0; /* The swap token gets in the way of swapout... */ if (!priority) disable_swap_token(); all_zones_ok = 1; 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 (!populated_zone(zone)) continue; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; if (!zone_watermark_ok(zone, order, zone->pages_high, 0, 0)) { end_zone = i; goto scan; } } goto out; } else { end_zone = pgdat->nr_zones - 1; } scan: for (i = 0; i <= end_zone; i++) { struct zone *zone = pgdat->node_zones + i; lru_pages += zone->nr_active + zone->nr_inactive; } /* * 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; int nr_slab; if (!populated_zone(zone)) continue; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; if (nr_pages == 0) { /* Not software suspend */ if (!zone_watermark_ok(zone, order, zone->pages_high, end_zone, 0)) all_zones_ok = 0; } zone->temp_priority = priority; if (zone->prev_priority > priority) zone->prev_priority = priority; sc.nr_scanned = 0; nr_reclaimed += shrink_zone(priority, zone, &sc); reclaim_state->reclaimed_slab = 0; nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages); nr_reclaimed += reclaim_state->reclaimed_slab; total_scanned += sc.nr_scanned; if (zone->all_unreclaimable) continue; if (nr_slab == 0 && zone->pages_scanned >= (zone->nr_active + zone->nr_inactive) * 4) 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 > nr_reclaimed + nr_reclaimed / 2) sc.may_writepage = 1; } if (nr_pages && to_free > nr_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); /* * We do this so kswapd doesn't build up large priorities for * example when it is freeing in parallel with allocators. It * matches the direct reclaim path behaviour in terms of impact * on zone->*_priority. */ if ((nr_reclaimed >= SWAP_CLUSTER_MAX) && !nr_pages) break; } out: for (i = 0; i < pgdat->nr_zones; i++) { struct zone *zone = pgdat->node_zones + i; zone->prev_priority = zone->temp_priority; } if (!all_zones_ok) { cond_resched(); goto loop_again; } return nr_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. */ static int kswapd(void *p) { unsigned long order; 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_SWAPWRITE | PF_KSWAPD; order = 0; for ( ; ; ) { unsigned long new_order; try_to_freeze(); prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); new_order = pgdat->kswapd_max_order; pgdat->kswapd_max_order = 0; if (order < new_order) { /* * Don't sleep if someone wants a larger 'order' * allocation */ order = new_order; } else { schedule(); order = pgdat->kswapd_max_order; } finish_wait(&pgdat->kswapd_wait, &wait); balance_pgdat(pgdat, 0, order); } return 0; } /* * A zone is low on free memory, so wake its kswapd task to service it. */ void wakeup_kswapd(struct zone *zone, int order) { pg_data_t *pgdat; if (!populated_zone(zone)) return; pgdat = zone->zone_pgdat; if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0)) return; if (pgdat->kswapd_max_order < order) pgdat->kswapd_max_order = order; if (!cpuset_zone_allowed(zone, __GFP_HARDWALL)) return; if (!waitqueue_active(&pgdat->kswapd_wait)) return; wake_up_interruptible(&pgdat->kswapd_wait); } #ifdef CONFIG_PM /* * Try to free `nr_pages' of memory, system-wide. Returns the number of freed * pages. */ unsigned long shrink_all_memory(unsigned long nr_pages) { pg_data_t *pgdat; unsigned long nr_to_free = nr_pages; unsigned long ret = 0; unsigned retry = 2; struct reclaim_state reclaim_state = { .reclaimed_slab = 0, }; current->reclaim_state = &reclaim_state; repeat: for_each_online_pgdat(pgdat) { unsigned long freed; freed = balance_pgdat(pgdat, nr_to_free, 0); ret += freed; nr_to_free -= freed; if ((long)nr_to_free <= 0) break; } if (retry-- && ret < nr_pages) { blk_congestion_wait(WRITE, HZ/5); goto repeat; } 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 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) { pg_data_t *pgdat; cpumask_t mask; if (action == CPU_ONLINE) { for_each_online_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_online_pgdat(pgdat) { pid_t pid; pid = kernel_thread(kswapd, pgdat, CLONE_KERNEL); BUG_ON(pid < 0); read_lock(&tasklist_lock); pgdat->kswapd = find_task_by_pid(pid); read_unlock(&tasklist_lock); } total_memory = nr_free_pagecache_pages(); hotcpu_notifier(cpu_callback, 0); return 0; } module_init(kswapd_init) #ifdef CONFIG_NUMA /* * Zone reclaim mode * * If non-zero call zone_reclaim when the number of free pages falls below * the watermarks. * * In the future we may add flags to the mode. However, the page allocator * should only have to check that zone_reclaim_mode != 0 before calling * zone_reclaim(). */ int zone_reclaim_mode __read_mostly; #define RECLAIM_OFF 0 #define RECLAIM_ZONE (1<<0) /* Run shrink_cache on the zone */ #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ #define RECLAIM_SLAB (1<<3) /* Do a global slab shrink if the zone is out of memory */ /* * Mininum time between zone reclaim scans */ int zone_reclaim_interval __read_mostly = 30*HZ; /* * Priority for ZONE_RECLAIM. This determines the fraction of pages * of a node considered for each zone_reclaim. 4 scans 1/16th of * a zone. */ #define ZONE_RECLAIM_PRIORITY 4 /* * Try to free up some pages from this zone through reclaim. */ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) { /* Minimum pages needed in order to stay on node */ const unsigned long nr_pages = 1 << order; struct task_struct *p = current; struct reclaim_state reclaim_state; int priority; unsigned long nr_reclaimed = 0; struct scan_control sc = { .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE), .may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP), .nr_mapped = read_page_state(nr_mapped), .swap_cluster_max = max_t(unsigned long, nr_pages, SWAP_CLUSTER_MAX), .gfp_mask = gfp_mask, }; disable_swap_token(); cond_resched(); /* * We need to be able to allocate from the reserves for RECLAIM_SWAP * and we also need to be able to write out pages for RECLAIM_WRITE * and RECLAIM_SWAP. */ p->flags |= PF_MEMALLOC | PF_SWAPWRITE; reclaim_state.reclaimed_slab = 0; p->reclaim_state = &reclaim_state; /* * Free memory by calling shrink zone with increasing priorities * until we have enough memory freed. */ priority = ZONE_RECLAIM_PRIORITY; do { nr_reclaimed += shrink_zone(priority, zone, &sc); priority--; } while (priority >= 0 && nr_reclaimed < nr_pages); if (nr_reclaimed < nr_pages && (zone_reclaim_mode & RECLAIM_SLAB)) { /* * shrink_slab() does not currently allow us to determine how * many pages were freed in this zone. So we just shake the slab * a bit and then go off node for this particular allocation * despite possibly having freed enough memory to allocate in * this zone. If we freed local memory then the next * allocations will be local again. * * shrink_slab will free memory on all zones and may take * a long time. */ shrink_slab(sc.nr_scanned, gfp_mask, order); } p->reclaim_state = NULL; current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE); if (nr_reclaimed == 0) { /* * We were unable to reclaim enough pages to stay on node. We * now allow off node accesses for a certain time period before * trying again to reclaim pages from the local zone. */ zone->last_unsuccessful_zone_reclaim = jiffies; } return nr_reclaimed >= nr_pages; } int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) { cpumask_t mask; int node_id; /* * Do not reclaim if there was a recent unsuccessful attempt at zone * reclaim. In that case we let allocations go off node for the * zone_reclaim_interval. Otherwise we would scan for each off-node * page allocation. */ if (time_before(jiffies, zone->last_unsuccessful_zone_reclaim + zone_reclaim_interval)) return 0; /* * Avoid concurrent zone reclaims, do not reclaim in a zone that does * not have reclaimable pages and if we should not delay the allocation * then do not scan. */ if (!(gfp_mask & __GFP_WAIT) || zone->all_unreclaimable || atomic_read(&zone->reclaim_in_progress) > 0 || (current->flags & PF_MEMALLOC)) return 0; /* * Only run zone reclaim on the local zone or on zones that do not * have associated processors. This will favor the local processor * over remote processors and spread off node memory allocations * as wide as possible. */ node_id = zone->zone_pgdat->node_id; mask = node_to_cpumask(node_id); if (!cpus_empty(mask) && node_id != numa_node_id()) return 0; return __zone_reclaim(zone, gfp_mask, order); } #endif