/*
* 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/suspend.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-locking.h>
#include <linux/topology.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/div64.h>
#include <linux/swapops.h>
/*
* From 0 .. 100. Higher means more swappy.
*/
int vm_swappiness = 60;
static long total_memory;
#ifdef ARCH_HAS_PREFETCH
#define prefetch_prev_lru_page(_page, _base, _field) \
do { \
if ((_page)->lru.prev != _base) { \
struct page *prev; \
\
prev = list_entry(_page->lru.prev, \
struct 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 = list_entry(_page->lru.prev, \
struct page, lru); \
prefetchw(&prev->_field); \
} \
} while (0)
#else
#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
#endif
/*
* The list of shrinker callbacks used by to apply pressure to
* ageable caches.
*/
struct shrinker {
shrinker_t shrinker;
struct list_head list;
int seeks; /* seeks to recreate an obj */
long nr; /* objs pending delete */
};
static LIST_HEAD(shrinker_list);
static DECLARE_MUTEX(shrinker_sem);
/*
* Add a shrinker callback to be called from the vm
*/
struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
{
struct shrinker *shrinker;
shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
if (shrinker) {
shrinker->shrinker = theshrinker;
shrinker->seeks = seeks;
shrinker->nr = 0;
down(&shrinker_sem);
list_add(&shrinker->list, &shrinker_list);
up(&shrinker_sem);
}
return shrinker;
}
EXPORT_SYMBOL(set_shrinker);
/*
* Remove one
*/
void remove_shrinker(struct shrinker *shrinker)
{
down(&shrinker_sem);
list_del(&shrinker->list);
up(&shrinker_sem);
kfree(shrinker);
}
EXPORT_SYMBOL(remove_shrinker);
#define SHRINK_BATCH 128
/*
* Call the shrink functions to age shrinkable caches
*
* Here we assume it costs one seek to replace a lru page and that it also
* takes a seek to recreate a cache object. With this in mind we age equal
* percentages of the lru and ageable caches. This should balance the seeks
* generated by these structures.
*
* If the vm encounted mapped pages on the LRU it increase the pressure on
* slab to avoid swapping.
*
* We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
*/
static int shrink_slab(long scanned, unsigned int gfp_mask)
{
struct shrinker *shrinker;
long pages;
if (down_trylock(&shrinker_sem))
return 0;
pages = nr_used_zone_pages();
list_for_each_entry(shrinker, &shrinker_list, list) {
unsigned long long delta;
delta = 4 * (scanned / shrinker->seeks);
delta *= (*shrinker->shrinker)(0, gfp_mask);
do_div(delta, pages + 1);
shrinker->nr += delta;
if (shrinker->nr > SHRINK_BATCH) {
long nr_to_scan = shrinker->nr;
shrinker->nr = 0;
while (nr_to_scan) {
long this_scan = nr_to_scan;
if (this_scan > 128)
this_scan = 128;
(*shrinker->shrinker)(this_scan, gfp_mask);
nr_to_scan -= this_scan;
cond_resched();
}
}
}
up(&shrinker_sem);
return 0;
}
/* Must be called with page's pte_chain_lock held. */
static inline int page_mapping_inuse(struct page *page)
{
struct address_space *mapping = page->mapping;
/* Page is in somebody's page tables. */
if (page_mapped(page))
return 1;
/* XXX: does this happen ? */
if (!mapping)
return 0;
/* Be more reluctant to reclaim swapcache than pagecache */
if (PageSwapCache(page))
return 1;
/* File is mmap'd by somebody. */
if (!list_empty(&mapping->i_mmap))
return 1;
if (!list_empty(&mapping->i_mmap_shared))
return 1;
return 0;
}
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 == mapping) {
if (error == -ENOSPC)
set_bit(AS_ENOSPC, &mapping->flags);
else
set_bit(AS_EIO, &mapping->flags);
}
unlock_page(page);
}
/*
* shrink_list returns the number of reclaimed pages
*/
static int
shrink_list(struct list_head *page_list, unsigned int gfp_mask,
int *max_scan, int *nr_mapped)
{
struct address_space *mapping;
LIST_HEAD(ret_pages);
struct pagevec freed_pvec;
int pgactivate = 0;
int ret = 0;
cond_resched();
pagevec_init(&freed_pvec, 1);
while (!list_empty(page_list)) {
struct page *page;
int may_enter_fs;
int referenced;
page = list_entry(page_list->prev, struct page, lru);
list_del(&page->lru);
if (TestSetPageLocked(page))
goto keep;
/* Double the slab pressure for mapped and swapcache pages */
if (page_mapped(page) || PageSwapCache(page))
(*nr_mapped)++;
BUG_ON(PageActive(page));
may_enter_fs = (gfp_mask & __GFP_FS) ||
(PageSwapCache(page) && (gfp_mask & __GFP_IO));
if (PageWriteback(page))
goto keep_locked;
pte_chain_lock(page);
referenced = page_referenced(page);
if (referenced && page_mapping_inuse(page)) {
/* In active use or really unfreeable. Activate it. */
pte_chain_unlock(page);
goto activate_locked;
}
mapping = page->mapping;
#ifdef CONFIG_SWAP
/*
* Anonymous process memory without backing store. Try to
* allocate it some swap space here.
*
* XXX: implement swap clustering ?
*/
if (page_mapped(page) && !mapping && !PagePrivate(page)) {
pte_chain_unlock(page);
if (!add_to_swap(page))
goto activate_locked;
pte_chain_lock(page);
mapping = page->mapping;
}
#endif /* CONFIG_SWAP */
/*
* 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:
pte_chain_unlock(page);
goto activate_locked;
case SWAP_AGAIN:
pte_chain_unlock(page);
goto keep_locked;
case SWAP_SUCCESS:
; /* try to free the page below */
}
}
pte_chain_unlock(page);
/*
* 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 (PageDirty(page)) {
if (referenced)
goto keep_locked;
if (!is_page_cache_freeable(page))
goto keep_locked;
if (!mapping)
goto keep_locked;
if (mapping->a_ops->writepage == NULL)
goto activate_locked;
if (!may_enter_fs)
goto keep_locked;
if (!may_write_to_queue(mapping->backing_dev_info))
goto keep_locked;
spin_lock(&mapping->page_lock);
if (test_clear_page_dirty(page)) {
int res;
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
.nr_to_write = SWAP_CLUSTER_MAX,
.nonblocking = 1,
.for_reclaim = 1,
};
list_move(&page->list, &mapping->locked_pages);
spin_unlock(&mapping->page_lock);
SetPageReclaim(page);
res = mapping->a_ops->writepage(page, &wbc);
if (res < 0)
handle_write_error(mapping, page, res);
if (res == WRITEPAGE_ACTIVATE) {
ClearPageReclaim(page);
goto activate_locked;
}
if (!PageWriteback(page)) {
/* synchronous write or broken a_ops? */
ClearPageReclaim(page);
}
goto keep;
}
spin_unlock(&mapping->page_lock);
}
/*
* 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 == 0) it can be freed.
* Otherwise, leave the page on the LRU so it is swappable.
*/
if (PagePrivate(page)) {
if (!try_to_release_page(page, gfp_mask))
goto activate_locked;
if (!mapping && page_count(page) == 1)
goto free_it;
}
if (!mapping)
goto keep_locked; /* truncate got there first */
spin_lock(&mapping->page_lock);
/*
* The non-racy check for busy page. It is critical to check
* PageDirty _after_ making sure that the page is freeable and
* not in use by anybody. (pagecache + us == 2)
*/
if (page_count(page) != 2 || PageDirty(page)) {
spin_unlock(&mapping->page_lock);
goto keep_locked;
}
#ifdef CONFIG_SWAP
if (PageSwapCache(page)) {
swp_entry_t swap = { .val = page->index };
__delete_from_swap_cache(page);
spin_unlock(&mapping->page_lock);
swap_free(swap);
__put_page(page); /* The pagecache ref */
goto free_it;
}
#endif /* CONFIG_SWAP */
__remove_from_page_cache(page);
spin_unlock(&mapping->page_lock);
__put_page(page);
free_it:
unlock_page(page);
ret++;
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(pgsteal, ret);
if (current_is_kswapd())
mod_page_state(kswapd_steal, ret);
mod_page_state(pgactivate, pgactivate);
return ret;
}
/*
* zone->lru_lock is heavily contented. We relieve it by quickly privatising
* a batch of pages and working on them outside the lock. Any pages which were
* not freed will be added back to the LRU.
*
* shrink_cache() is passed the number of pages to try to free, and returns
* the number of pages which were reclaimed.
*
* For pagecache intensive workloads, the first loop here is the hottest spot
* in the kernel (apart from the copy_*_user functions).
*/
static int
shrink_cache(const int nr_pages, struct zone *zone,
unsigned int gfp_mask, int max_scan, int *nr_mapped)
{
LIST_HEAD(page_list);
struct pagevec pvec;
int nr_to_process;
int ret = 0;
/*
* Try to ensure that we free `nr_pages' pages in one pass of the loop.
*/
nr_to_process = nr_pages;
if (nr_to_process < SWAP_CLUSTER_MAX)
nr_to_process = SWAP_CLUSTER_MAX;
pagevec_init(&pvec, 1);
lru_add_drain();
spin_lock_irq(&zone->lru_lock);
while (max_scan > 0 && ret < nr_pages) {
struct page *page;
int nr_taken = 0;
int nr_scan = 0;
int nr_freed;
while (nr_scan++ < nr_to_process &&
!list_empty(&zone->inactive_list)) {
page = list_entry(zone->inactive_list.prev,
struct page, lru);
prefetchw_prev_lru_page(page,
&zone->inactive_list, flags);
if (!TestClearPageLRU(page))
BUG();
list_del(&page->lru);
if (page_count(page) == 0) {
/* It is currently in pagevec_release() */
SetPageLRU(page);
list_add(&page->lru, &zone->inactive_list);
continue;
}
list_add(&page->lru, &page_list);
page_cache_get(page);
nr_taken++;
}
zone->nr_inactive -= nr_taken;
zone->pages_scanned += nr_taken;
spin_unlock_irq(&zone->lru_lock);
if (nr_taken == 0)
goto done;
max_scan -= nr_scan;
mod_page_state(pgscan, nr_scan);
nr_freed = shrink_list(&page_list, gfp_mask,
&max_scan, nr_mapped);
ret += nr_freed;
if (nr_freed <= 0 && list_empty(&page_list))
goto done;
spin_lock_irq(&zone->lru_lock);
/*
* Put back any unfreeable pages.
*/
while (!list_empty(&page_list)) {
page = list_entry(page_list.prev, struct page, lru);
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);
return ret;
}
/*
* 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, const int nr_pages_in,
struct page_state *ps, int priority)
{
int pgmoved;
int pgdeactivate = 0;
int nr_pages = nr_pages_in;
LIST_HEAD(l_hold); /* The pages which were snipped off */
LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */
LIST_HEAD(l_active); /* Pages to go onto the active_list */
struct page *page;
struct pagevec pvec;
int reclaim_mapped = 0;
long mapped_ratio;
long distress;
long swap_tendency;
lru_add_drain();
pgmoved = 0;
spin_lock_irq(&zone->lru_lock);
while (nr_pages && !list_empty(&zone->active_list)) {
page = list_entry(zone->active_list.prev, struct page, lru);
prefetchw_prev_lru_page(page, &zone->active_list, flags);
if (!TestClearPageLRU(page))
BUG();
list_del(&page->lru);
if (page_count(page) == 0) {
/* It is currently in pagevec_release() */
SetPageLRU(page);
list_add(&page->lru, &zone->active_list);
} else {
page_cache_get(page);
list_add(&page->lru, &l_hold);
pgmoved++;
}
nr_pages--;
}
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 = (ps->nr_mapped * 100) / total_memory;
/*
* Now decide how much we really want to unmap some pages. The mapped
* ratio is downgraded - just because there's a lot of mapped memory
* doesn't necessarily mean that page reclaim isn't succeeding.
*
* The distress ratio is important - we don't want to start going oom.
*
* A 100% value of vm_swappiness overrides this algorithm altogether.
*/
swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
/*
* Now use this metric to decide whether to start moving mapped memory
* onto the inactive list.
*/
if (swap_tendency >= 100)
reclaim_mapped = 1;
while (!list_empty(&l_hold)) {
page = list_entry(l_hold.prev, struct page, lru);
list_del(&page->lru);
if (page_mapped(page)) {
pte_chain_lock(page);
if (page_mapped(page) && page_referenced(page)) {
pte_chain_unlock(page);
list_add(&page->lru, &l_active);
continue;
}
pte_chain_unlock(page);
if (!reclaim_mapped) {
list_add(&page->lru, &l_active);
continue;
}
}
/*
* FIXME: need to consider page_count(page) here if/when we
* reap orphaned pages via the LRU (Daniel's locking stuff)
*/
if (total_swap_pages == 0 && !page->mapping &&
!PagePrivate(page)) {
list_add(&page->lru, &l_active);
continue;
}
list_add(&page->lru, &l_inactive);
}
pagevec_init(&pvec, 1);
pgmoved = 0;
spin_lock_irq(&zone->lru_lock);
while (!list_empty(&l_inactive)) {
page = list_entry(l_inactive.prev, struct page, lru);
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 = list_entry(l_active.prev, struct page, lru);
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(pgrefill, nr_pages_in - nr_pages);
mod_page_state(pgdeactivate, pgdeactivate);
}
/*
* Try to reclaim `nr_pages' from this zone. Returns the number of reclaimed
* pages. This is a basic per-zone page freer. Used by both kswapd and
* direct reclaim.
*/
static int
shrink_zone(struct zone *zone, int max_scan, unsigned int gfp_mask,
const int nr_pages, int *nr_mapped, struct page_state *ps, int priority)
{
unsigned long ratio;
/*
* Try to keep the active list 2/3 of the size of the cache. And
* make sure that refill_inactive is given a decent number of pages.
*
* The "ratio+1" here is important. With pagecache-intensive workloads
* the inactive list is huge, and `ratio' evaluates to zero all the
* time. Which pins the active list memory. So we add one to `ratio'
* just to make sure that the kernel will slowly sift through the
* active list.
*/
ratio = (unsigned long)nr_pages * zone->nr_active /
((zone->nr_inactive | 1) * 2);
atomic_add(ratio+1, &zone->refill_counter);
if (atomic_read(&zone->refill_counter) > SWAP_CLUSTER_MAX) {
int count;
/*
* Don't try to bring down too many pages in one attempt.
* If this fails, the caller will increase `priority' and
* we'll try again, with an increased chance of reclaiming
* mapped memory.
*/
count = atomic_read(&zone->refill_counter);
if (count > SWAP_CLUSTER_MAX * 4)
count = SWAP_CLUSTER_MAX * 4;
atomic_set(&zone->refill_counter, 0);
refill_inactive_zone(zone, count, ps, priority);
}
return shrink_cache(nr_pages, zone, gfp_mask,
max_scan, nr_mapped);
}
/*
* 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 int
shrink_caches(struct zone **zones, int priority, int *total_scanned,
int gfp_mask, int nr_pages, struct page_state *ps)
{
int ret = 0;
int i;
for (i = 0; zones[i] != NULL; i++) {
int to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX);
struct zone *zone = zones[i];
int nr_mapped = 0;
int max_scan;
if (zone->free_pages < zone->pages_high)
zone->temp_priority = priority;
if (zone->all_unreclaimable && priority != DEF_PRIORITY)
continue; /* Let kswapd poll it */
/*
* If we cannot reclaim `nr_pages' pages by scanning twice
* that many pages then fall back to the next zone.
*/
max_scan = zone->nr_inactive >> priority;
if (max_scan < to_reclaim * 2)
max_scan = to_reclaim * 2;
ret += shrink_zone(zone, max_scan, gfp_mask,
to_reclaim, &nr_mapped, ps, priority);
*total_scanned += max_scan + nr_mapped;
if (ret >= nr_pages)
break;
}
return ret;
}
/*
* 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. So for !__GFP_FS callers, we just perform a
* small LRU walk and if that didn't work out, fail the allocation back to the
* caller. GFP_NOFS allocators need to know how to deal with it. Kicking
* bdflush, waiting and retrying will work.
*
* This is a fairly lame algorithm - it can result in excessive CPU burning and
* excessive rotation of the inactive list, which is _supposed_ to be an LRU,
* yes?
*/
int try_to_free_pages(struct zone **zones,
unsigned int gfp_mask, unsigned int order)
{
int priority;
int ret = 0;
const int nr_pages = SWAP_CLUSTER_MAX;
int nr_reclaimed = 0;
struct reclaim_state *reclaim_state = current->reclaim_state;
int i;
inc_page_state(allocstall);
for (i = 0; zones[i] != 0; i++)
zones[i]->temp_priority = DEF_PRIORITY;
for (priority = DEF_PRIORITY; priority >= 0; priority--) {
int total_scanned = 0;
struct page_state ps;
get_page_state(&ps);
nr_reclaimed += shrink_caches(zones, priority, &total_scanned,
gfp_mask, nr_pages, &ps);
if (nr_reclaimed >= nr_pages) {
ret = 1;
goto out;
}
if (!(gfp_mask & __GFP_FS))
break; /* Let the caller handle it */
/*
* Try to write back as many pages as we just scanned. Not
* sure if that makes sense, but it's an attempt to avoid
* creating IO storms unnecessarily
*/
wakeup_bdflush(total_scanned);
/* Take a nap, wait for some writeback to complete */
blk_congestion_wait(WRITE, HZ/10);
if (zones[0] - zones[0]->zone_pgdat->node_zones < ZONE_HIGHMEM) {
shrink_slab(total_scanned, gfp_mask);
if (reclaim_state) {
nr_reclaimed += reclaim_state->reclaimed_slab;
reclaim_state->reclaimed_slab = 0;
}
}
}
if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY))
out_of_memory();
out:
for (i = 0; zones[i] != 0; i++)
zones[i]->prev_priority = zones[i]->temp_priority;
return ret;
}
/*
* For kswapd, balance_pgdat() will work across all this node's zones until
* they are all at pages_high.
*
* If `nr_pages' is non-zero then it is the number of pages which are to be
* reclaimed, regardless of the zone occupancies. This is a software suspend
* special.
*
* Returns the number of pages which were actually freed.
*
* There is special handling here for zones which are full of pinned pages.
* This can happen if the pages are all mlocked, or if they are all used by
* device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
* What we do is to detect the case where all pages in the zone have been
* scanned twice and there has been zero successful reclaim. Mark the zone as
* dead and from now on, only perform a short scan. Basically we're polling
* the zone for when the problem goes away.
*/
static int balance_pgdat(pg_data_t *pgdat, int nr_pages, struct page_state *ps)
{
int to_free = nr_pages;
int priority;
int i;
struct reclaim_state *reclaim_state = current->reclaim_state;
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; priority--) {
int all_zones_ok = 1;
for (i = 0; i < pgdat->nr_zones; i++) {
struct zone *zone = pgdat->node_zones + i;
int nr_mapped = 0;
int max_scan;
int to_reclaim;
if (zone->all_unreclaimable && priority != DEF_PRIORITY)
continue;
if (nr_pages && to_free > 0) { /* Software suspend */
to_reclaim = min(to_free, SWAP_CLUSTER_MAX*8);
} else { /* Zone balancing */
to_reclaim = zone->pages_high-zone->free_pages;
if (to_reclaim <= 0)
continue;
}
zone->temp_priority = priority;
all_zones_ok = 0;
max_scan = zone->nr_inactive >> priority;
if (max_scan < to_reclaim * 2)
max_scan = to_reclaim * 2;
if (max_scan < SWAP_CLUSTER_MAX)
max_scan = SWAP_CLUSTER_MAX;
to_free -= shrink_zone(zone, max_scan, GFP_KERNEL,
to_reclaim, &nr_mapped, ps, priority);
if (i < ZONE_HIGHMEM) {
reclaim_state->reclaimed_slab = 0;
shrink_slab(max_scan + nr_mapped, GFP_KERNEL);
to_free -= reclaim_state->reclaimed_slab;
}
if (zone->all_unreclaimable)
continue;
if (zone->pages_scanned > zone->present_pages * 2)
zone->all_unreclaimable = 1;
}
if (all_zones_ok)
break;
if (to_free > 0)
blk_congestion_wait(WRITE, HZ/10);
}
for (i = 0; i < pgdat->nr_zones; i++) {
struct zone *zone = pgdat->node_zones + i;
zone->prev_priority = zone->temp_priority;
}
return nr_pages - to_free;
}
/*
* The background pageout daemon, started as a kernel thread
* from the init process.
*
* This basically trickles out pages so that we have _some_
* free memory available even if there is no other activity
* that frees anything up. This is needed for things like routing
* etc, where we otherwise might have all activity going on in
* asynchronous contexts that cannot page things out.
*
* If there are applications that are active memory-allocators
* (most normal use), this basically shouldn't matter.
*/
int kswapd(void *p)
{
pg_data_t *pgdat = (pg_data_t*)p;
struct task_struct *tsk = current;
DEFINE_WAIT(wait);
struct reclaim_state reclaim_state = {
.reclaimed_slab = 0,
};
cpumask_t cpumask;
daemonize("kswapd%d", pgdat->node_id);
cpumask = node_to_cpumask(pgdat->node_id);
if (!cpus_empty(cpumask))
set_cpus_allowed(tsk, cpumask);
current->reclaim_state = &reclaim_state;
/*
* Tell the memory management that we're a "memory allocator",
* and that if we need more memory we should get access to it
* regardless (see "__alloc_pages()"). "kswapd" should
* never get caught in the normal page freeing logic.
*
* (Kswapd normally doesn't need memory anyway, but sometimes
* you need a small amount of memory in order to be able to
* page out something else, and this flag essentially protects
* us from recursively trying to free more memory as we're
* trying to free the first piece of memory in the first place).
*/
tsk->flags |= PF_MEMALLOC|PF_KSWAPD;
for ( ; ; ) {
struct page_state ps;
if (current->flags & PF_FREEZE)
refrigerator(PF_IOTHREAD);
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
schedule();
finish_wait(&pgdat->kswapd_wait, &wait);
get_page_state(&ps);
balance_pgdat(pgdat, 0, &ps);
}
}
/*
* A zone is low on free memory, so wake its kswapd task to service it.
*/
void wakeup_kswapd(struct zone *zone)
{
if (zone->free_pages > zone->pages_low)
return;
if (!waitqueue_active(&zone->zone_pgdat->kswapd_wait))
return;
wake_up_interruptible(&zone->zone_pgdat->kswapd_wait);
}
#ifdef CONFIG_PM
/*
* Try to free `nr_pages' of memory, system-wide. Returns the number of freed
* pages.
*/
int shrink_all_memory(int nr_pages)
{
pg_data_t *pgdat;
int nr_to_free = nr_pages;
int ret = 0;
struct reclaim_state reclaim_state = {
.reclaimed_slab = 0,
};
current->reclaim_state = &reclaim_state;
for_each_pgdat(pgdat) {
int freed;
struct page_state ps;
get_page_state(&ps);
freed = balance_pgdat(pgdat, nr_to_free, &ps);
ret += freed;
nr_to_free -= freed;
if (nr_to_free <= 0)
break;
}
current->reclaim_state = NULL;
return ret;
}
#endif
static int __init kswapd_init(void)
{
pg_data_t *pgdat;
swap_setup();
for_each_pgdat(pgdat)
kernel_thread(kswapd, pgdat, CLONE_KERNEL);
total_memory = nr_free_pagecache_pages();
return 0;
}
module_init(kswapd_init)
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