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memcg: simplify corner case handling of LRU.

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This patch simplifies LRU handling of racy case (memcg+SwapCache).  At
charging, SwapCache tend to be on LRU already.  So, before overwriting
pc->mem_cgroup, the page must be removed from LRU and added to LRU
later.

This patch does
        spin_lock(zone->lru_lock);
        if (PageLRU(page))
                remove from LRU
        overwrite pc->mem_cgroup
        if (PageLRU(page))
                add to new LRU.
        spin_unlock(zone->lru_lock);

And guarantee all pages are not on LRU at modifying pc->mem_cgroup.
This patch also unfies lru handling of replace_page_cache() and
swapin.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Ying Han <yinghan@google.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KAMEZAWA Hiroyuki 2012-01-12 17:18:57 -08:00 committed by Linus Torvalds
parent dc67d50465
commit 36b62ad539
1 changed files with 16 additions and 93 deletions
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109
mm/memcontrol.c
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@ -1136,86 +1136,6 @@ struct lruvec *mem_cgroup_lru_move_lists(struct zone *zone,
return mem_cgroup_lru_add_list(zone, page, to);
}
/*
* At handling SwapCache and other FUSE stuff, pc->mem_cgroup may be changed
* while it's linked to lru because the page may be reused after it's fully
* uncharged. To handle that, unlink page_cgroup from LRU when charge it again.
* It's done under lock_page and expected that zone->lru_lock isnever held.
*/
static void mem_cgroup_lru_del_before_commit(struct page *page)
{
enum lru_list lru;
unsigned long flags;
struct zone *zone = page_zone(page);
struct page_cgroup *pc = lookup_page_cgroup(page);
/*
* Doing this check without taking ->lru_lock seems wrong but this
* is safe. Because if page_cgroup's USED bit is unset, the page
* will not be added to any memcg's LRU. If page_cgroup's USED bit is
* set, the commit after this will fail, anyway.
* This all charge/uncharge is done under some mutual execustion.
* So, we don't need to taking care of changes in USED bit.
*/
if (likely(!PageLRU(page)))
return;
spin_lock_irqsave(&zone->lru_lock, flags);
lru = page_lru(page);
/*
* The uncharged page could still be registered to the LRU of
* the stale pc->mem_cgroup.
*
* As pc->mem_cgroup is about to get overwritten, the old LRU
* accounting needs to be taken care of. Let root_mem_cgroup
* babysit the page until the new memcg is responsible for it.
*
* The PCG_USED bit is guarded by lock_page() as the page is
* swapcache/pagecache.
*/
if (PageLRU(page) && PageCgroupAcctLRU(pc) && !PageCgroupUsed(pc)) {
del_page_from_lru_list(zone, page, lru);
add_page_to_lru_list(zone, page, lru);
}
spin_unlock_irqrestore(&zone->lru_lock, flags);
}
static void mem_cgroup_lru_add_after_commit(struct page *page)
{
enum lru_list lru;
unsigned long flags;
struct zone *zone = page_zone(page);
struct page_cgroup *pc = lookup_page_cgroup(page);
/*
* putback: charge:
* SetPageLRU SetPageCgroupUsed
* smp_mb smp_mb
* PageCgroupUsed && add to memcg LRU PageLRU && add to memcg LRU
*
* Ensure that one of the two sides adds the page to the memcg
* LRU during a race.
*/
smp_mb();
/* taking care of that the page is added to LRU while we commit it */
if (likely(!PageLRU(page)))
return;
spin_lock_irqsave(&zone->lru_lock, flags);
lru = page_lru(page);
/*
* If the page is not on the LRU, someone will soon put it
* there. If it is, and also already accounted for on the
* memcg-side, it must be on the right lruvec as setting
* pc->mem_cgroup and PageCgroupUsed is properly ordered.
* Otherwise, root_mem_cgroup has been babysitting the page
* during the charge. Move it to the new memcg now.
*/
if (PageLRU(page) && !PageCgroupAcctLRU(pc)) {
del_page_from_lru_list(zone, page, lru);
add_page_to_lru_list(zone, page, lru);
}
spin_unlock_irqrestore(&zone->lru_lock, flags);
}
/*
* Checks whether given mem is same or in the root_mem_cgroup's
* hierarchy subtree
@ -2775,14 +2695,27 @@ __mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *memcg,
enum charge_type ctype)
{
struct page_cgroup *pc = lookup_page_cgroup(page);
struct zone *zone = page_zone(page);
unsigned long flags;
bool removed = false;
/*
* In some case, SwapCache, FUSE(splice_buf->radixtree), the page
* is already on LRU. It means the page may on some other page_cgroup's
* LRU. Take care of it.
*/
mem_cgroup_lru_del_before_commit(page);
spin_lock_irqsave(&zone->lru_lock, flags);
if (PageLRU(page)) {
del_page_from_lru_list(zone, page, page_lru(page));
ClearPageLRU(page);
removed = true;
}
__mem_cgroup_commit_charge(memcg, page, 1, pc, ctype);
mem_cgroup_lru_add_after_commit(page);
if (removed) {
add_page_to_lru_list(zone, page, page_lru(page));
SetPageLRU(page);
}
spin_unlock_irqrestore(&zone->lru_lock, flags);
return;
}
@ -3383,9 +3316,7 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
{
struct mem_cgroup *memcg;
struct page_cgroup *pc;
struct zone *zone;
enum charge_type type = MEM_CGROUP_CHARGE_TYPE_CACHE;
unsigned long flags;
if (mem_cgroup_disabled())
return;
@ -3401,20 +3332,12 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
if (PageSwapBacked(oldpage))
type = MEM_CGROUP_CHARGE_TYPE_SHMEM;
zone = page_zone(newpage);
pc = lookup_page_cgroup(newpage);
/*
* Even if newpage->mapping was NULL before starting replacement,
* the newpage may be on LRU(or pagevec for LRU) already. We lock
* LRU while we overwrite pc->mem_cgroup.
*/
spin_lock_irqsave(&zone->lru_lock, flags);
if (PageLRU(newpage))
del_page_from_lru_list(zone, newpage, page_lru(newpage));
__mem_cgroup_commit_charge(memcg, newpage, 1, pc, type);
if (PageLRU(newpage))
add_page_to_lru_list(zone, newpage, page_lru(newpage));
spin_unlock_irqrestore(&zone->lru_lock, flags);
__mem_cgroup_commit_charge_lrucare(newpage, memcg, type);
}
#ifdef CONFIG_DEBUG_VM