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vmscan.c
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vmscan.c
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/*
* 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 ([email protected]).
* 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;