linux-sg2042/mm/vmscan.c

1579 lines
41 KiB
C

/*
* 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 */
/* Ask shrink_caches, or shrink_zone to scan at this priority */
unsigned int priority;
/* This context's GFP mask */
gfp_t 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.
*
* Returns the number of slab objects which we shrunk.
*/
int shrink_slab(unsigned long scanned, gfp_t gfp_mask, unsigned long lru_pages)
{
struct shrinker *shrinker;
int 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_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 (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;
}
static 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_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);
/* 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)) {
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 (!remove_mapping(mapping, page))
goto keep_locked;
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;
}
#ifdef CONFIG_MIGRATION
static inline void move_to_lru(struct page *page)
{
list_del(&page->lru);
if (PageActive(page)) {
/*
* lru_cache_add_active checks that
* the PG_active bit is off.
*/
ClearPageActive(page);
lru_cache_add_active(page);
} else {
lru_cache_add(page);
}
put_page(page);
}
/*
* Add isolated pages on the list back to the LRU
*
* returns the number of pages put back.
*/
int putback_lru_pages(struct list_head *l)
{
struct page *page;
struct page *page2;
int count = 0;
list_for_each_entry_safe(page, page2, l, lru) {
move_to_lru(page);
count++;
}
return count;
}
/*
* swapout a single page
* page is locked upon entry, unlocked on exit
*/
static int swap_page(struct page *page)
{
struct address_space *mapping = page_mapping(page);
if (page_mapped(page) && mapping)
if (try_to_unmap(page) != SWAP_SUCCESS)
goto unlock_retry;
if (PageDirty(page)) {
/* Page is dirty, try to write it out here */
switch(pageout(page, mapping)) {
case PAGE_KEEP:
case PAGE_ACTIVATE:
goto unlock_retry;
case PAGE_SUCCESS:
goto retry;
case PAGE_CLEAN:
; /* try to free the page below */
}
}
if (PagePrivate(page)) {
if (!try_to_release_page(page, GFP_KERNEL) ||
(!mapping && page_count(page) == 1))
goto unlock_retry;
}
if (remove_mapping(mapping, page)) {
/* Success */
unlock_page(page);
return 0;
}
unlock_retry:
unlock_page(page);
retry:
return -EAGAIN;
}
/*
* migrate_pages
*
* Two lists are passed to this function. The first list
* contains the pages isolated from the LRU to be migrated.
* The second list contains new pages that the pages isolated
* can be moved to. If the second list is NULL then all
* pages are swapped out.
*
* The function returns after 10 attempts or if no pages
* are movable anymore because t has become empty
* or no retryable pages exist anymore.
*
* SIMPLIFIED VERSION: This implementation of migrate_pages
* is only swapping out pages and never touches the second
* list. The direct migration patchset
* extends this function to avoid the use of swap.
*
* Return: Number of pages not migrated when "to" ran empty.
*/
int migrate_pages(struct list_head *from, struct list_head *to,
struct list_head *moved, struct list_head *failed)
{
int retry;
int nr_failed = 0;
int pass = 0;
struct page *page;
struct page *page2;
int swapwrite = current->flags & PF_SWAPWRITE;
int rc;
if (!swapwrite)
current->flags |= PF_SWAPWRITE;
redo:
retry = 0;
list_for_each_entry_safe(page, page2, from, lru) {
cond_resched();
rc = 0;
if (page_count(page) == 1)
/* page was freed from under us. So we are done. */
goto next;
/*
* Skip locked pages during the first two passes to give the
* functions holding the lock time to release the page. Later we
* use lock_page() to have a higher chance of acquiring the
* lock.
*/
rc = -EAGAIN;
if (pass > 2)
lock_page(page);
else
if (TestSetPageLocked(page))
goto next;
/*
* Only wait on writeback if we have already done a pass where
* we we may have triggered writeouts for lots of pages.
*/
if (pass > 0) {
wait_on_page_writeback(page);
} else {
if (PageWriteback(page))
goto unlock_page;
}
/*
* Anonymous pages must have swap cache references otherwise
* the information contained in the page maps cannot be
* preserved.
*/
if (PageAnon(page) && !PageSwapCache(page)) {
if (!add_to_swap(page, GFP_KERNEL)) {
rc = -ENOMEM;
goto unlock_page;
}
}
/*
* Page is properly locked and writeback is complete.
* Try to migrate the page.
*/
rc = swap_page(page);
goto next;
unlock_page:
unlock_page(page);
next:
if (rc == -EAGAIN) {
retry++;
} else if (rc) {
/* Permanent failure */
list_move(&page->lru, failed);
nr_failed++;
} else {
/* Success */
list_move(&page->lru, moved);
}
}
if (retry && pass++ < 10)
goto redo;
if (!swapwrite)
current->flags &= ~PF_SWAPWRITE;
return nr_failed + retry;
}
static void lru_add_drain_per_cpu(void *dummy)
{
lru_add_drain();
}
/*
* Isolate one page from the LRU lists and put it on the
* indicated list. Do necessary cache draining if the
* page is not on the LRU lists yet.
*
* Result:
* 0 = page not on LRU list
* 1 = page removed from LRU list and added to the specified list.
* -ENOENT = page is being freed elsewhere.
*/
int isolate_lru_page(struct page *page)
{
int rc = 0;
struct zone *zone = page_zone(page);
redo:
spin_lock_irq(&zone->lru_lock);
rc = __isolate_lru_page(page);
if (rc == 1) {
if (PageActive(page))
del_page_from_active_list(zone, page);
else
del_page_from_inactive_list(zone, page);
}
spin_unlock_irq(&zone->lru_lock);
if (rc == 0) {
/*
* Maybe this page is still waiting for a cpu to drain it
* from one of the lru lists?
*/
rc = schedule_on_each_cpu(lru_add_drain_per_cpu, NULL);
if (rc == 0 && PageLRU(page))
goto redo;
}
return rc;
}
#endif
/*
* 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);
switch (__isolate_lru_page(page)) {
case 1:
/* Succeeded to isolate page */
list_move(&page->lru, dst);
nr_taken++;
break;
case -ENOENT:
/* Not possible to isolate */
list_move(&page->lru, src);
break;
default:
BUG();
}
}
*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;
nr_freed = shrink_list(&page_list, sc);
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);
spin_lock(&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)) {
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(&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 void
shrink_zone(struct zone *zone, struct scan_control *sc)
{
unsigned long nr_active;
unsigned long nr_inactive;
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 >> 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;
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);
}
}
throttle_vm_writeout();
atomic_dec(&zone->reclaim_in_progress);
}
/*
* 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 (!populated_zone(zone))
continue;
if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
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, gfp_t gfp_mask)
{
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, __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;
sc.nr_reclaimed = 0;
sc.priority = priority;
sc.swap_cluster_max = SWAP_CLUSTER_MAX;
if (!priority)
disable_swap_token();
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_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 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;
/* 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;
sc.nr_reclaimed = 0;
sc.priority = priority;
sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX;
atomic_inc(&zone->reclaim_in_progress);
shrink_zone(zone, &sc);
atomic_dec(&zone->reclaim_in_progress);
reclaim_state->reclaimed_slab = 0;
nr_slab = 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 (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 > 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_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.
*/
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)