diff options
Diffstat (limited to 'mm/vmscan.c')
| -rw-r--r-- | mm/vmscan.c | 1311 |
1 files changed, 1311 insertions, 0 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c new file mode 100644 index 0000000..4003c05 --- /dev/null +++ b/mm/vmscan.c @@ -0,0 +1,1311 @@ +/* + * 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 <asm/tlbflush.h> +#include <asm/div64.h> + +#include <linux/swapops.h> + +/* 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; + +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 */ + + /* How many pages shrink_cache() should reclaim */ + int nr_to_reclaim; + + /* 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; + + /* 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. + */ +static int shrink_slab(unsigned long scanned, unsigned int gfp_mask, + unsigned long lru_pages) +{ + struct shrinker *shrinker; + + if (scanned == 0) + scanned = SWAP_CLUSTER_MAX; + + if (!down_read_trylock(&shrinker_rwsem)) + return 0; + + list_for_each_entry(shrinker, &shrinker_list, list) { + unsigned long long delta; + unsigned long total_scan; + + delta = (4 * scanned) / shrinker->seeks; + delta *= (*shrinker->shrinker)(0, gfp_mask); + do_div(delta, lru_pages + 1); + shrinker->nr += delta; + if (shrinker->nr < 0) + shrinker->nr = LONG_MAX; /* It wrapped! */ + + total_scan = shrinker->nr; + shrinker->nr = 0; + + while (total_scan >= SHRINK_BATCH) { + long this_scan = SHRINK_BATCH; + int shrink_ret; + + shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask); + if (shrink_ret == -1) + break; + mod_page_state(slabs_scanned, this_scan); + total_scan -= this_scan; + + cond_resched(); + } + + shrinker->nr += total_scan; + } + up_read(&shrinker_rwsem); + return 0; +} + +/* 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_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); +} + +/* + * 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) { + /* + * Some data journaling orphaned pages can have + * page->mapping == NULL while being dirty with clean buffers. + */ + if (PageDirty(page) && 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 == WRITEPAGE_ACTIVATE) { + ClearPageReclaim(page); + return PAGE_ACTIVATE; + } + if (!PageWriteback(page)) { + /* synchronous write or broken a_ops? */ + ClearPageReclaim(page); + } + + return PAGE_SUCCESS; + } + + return PAGE_CLEAN; +} + +/* + * 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; + + cond_resched(); + + page = lru_to_page(page_list); + list_del(&page->lru); + + if (TestSetPageLocked(page)) + goto keep; + + BUG_ON(PageActive(page)); + + sc->nr_scanned++; + /* 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, sc->priority <= 0); + /* 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)) + 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)) { + 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 (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 */ + + 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 (page_count(page) != 2 || PageDirty(page)) { + write_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); + write_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); + write_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 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 int isolate_lru_pages(int nr_to_scan, struct list_head *src, + struct list_head *dst, int *scanned) +{ + int nr_taken = 0; + struct page *page; + int scan = 0; + + while (scan++ < nr_to_scan && !list_empty(src)) { + page = lru_to_page(src); + prefetchw_prev_lru_page(page, src, 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, src); + continue; + } else { + list_add(&page->lru, dst); + nr_taken++; + } + } + + *scanned = scan; + return nr_taken; +} + +/* + * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed + */ +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; + int nr_scan; + int 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); + + 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); + sc->nr_to_reclaim -= 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; + 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(); + 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); + + /* + * `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)) { + 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, sc->priority <= 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); + 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); +} + +/* + * 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 nr_active; + unsigned long nr_inactive; + + /* + * 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 >> sc->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 >> sc->priority) + 1; + nr_inactive = zone->nr_scan_inactive; + if (nr_inactive >= sc->swap_cluster_max) + zone->nr_scan_inactive = 0; + else + nr_inactive = 0; + + sc->nr_to_reclaim = sc->swap_cluster_max; + + while (nr_active || nr_inactive) { + if (nr_active) { + sc->nr_to_scan = min(nr_active, + (unsigned long)sc->swap_cluster_max); + nr_active -= sc->nr_to_scan; + refill_inactive_zone(zone, sc); + } + + if (nr_inactive) { + sc->nr_to_scan = min(nr_inactive, + (unsigned long)sc->swap_cluster_max); + nr_inactive -= sc->nr_to_scan; + shrink_cache(zone, sc); + if (sc->nr_to_reclaim <= 0) + break; + } + } + + throttle_vm_writeout(); +} + +/* + * 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]; + + if (zone->present_pages == 0) + continue; + + if (!cpuset_zone_allowed(zone)) + continue; + + 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; + unsigned long lru_pages = 0; + int i; + + sc.gfp_mask = gfp_mask; + sc.may_writepage = 0; + + inc_page_state(allocstall); + + for (i = 0; zones[i] != NULL; i++) { + struct zone *zone = zones[i]; + + if (!cpuset_zone_allowed(zone)) + 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; + sc.nr_reclaimed = 0; + sc.priority = priority; + sc.swap_cluster_max = SWAP_CLUSTER_MAX; + shrink_caches(zones, &sc); + shrink_slab(sc.nr_scanned, gfp_mask, lru_pages); + if (reclaim_state) { + sc.nr_reclaimed += reclaim_state->reclaimed_slab; + reclaim_state->reclaimed_slab = 0; + } + total_scanned += sc.nr_scanned; + total_reclaimed += sc.nr_reclaimed; + if (total_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_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); + } +out: + for (i = 0; zones[i] != 0; i++) { + struct zone *zone = zones[i]; + + if (!cpuset_zone_allowed(zone)) + 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 int balance_pgdat(pg_data_t *pgdat, int nr_pages, int order) +{ + int to_free = nr_pages; + int all_zones_ok; + int priority; + int i; + int total_scanned, total_reclaimed; + struct reclaim_state *reclaim_state = current->reclaim_state; + struct scan_control sc; + +loop_again: + total_scanned = 0; + total_reclaimed = 0; + 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 end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ + unsigned long lru_pages = 0; + + 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 (zone->present_pages == 0) + continue; + + if (zone->all_unreclaimable && + priority != DEF_PRIORITY) + continue; + + if (!zone_watermark_ok(zone, order, + zone->pages_high, 0, 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; + + if (zone->present_pages == 0) + 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, 0)) + 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; + sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX; + shrink_zone(zone, &sc); + reclaim_state->reclaimed_slab = 0; + shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages); + sc.nr_reclaimed += reclaim_state->reclaimed_slab; + total_reclaimed += sc.nr_reclaimed; + total_scanned += sc.nr_scanned; + if (zone->all_unreclaimable) + continue; + if (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 > 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); + + /* + * 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 ((total_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 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. + */ +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_KSWAPD; + + order = 0; + for ( ; ; ) { + unsigned long new_order; + if (current->flags & PF_FREEZE) + refrigerator(PF_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 (zone->present_pages == 0) + return; + + pgdat = zone->zone_pgdat; + if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0, 0)) + return; + if (pgdat->kswapd_max_order < order) + pgdat->kswapd_max_order = order; + if (!cpuset_zone_allowed(zone)) + 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, 0); + 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) |
