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memcg: remove a redundant check

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Because of remove refcnt patch, it's very rare case to that
mem_cgroup_charge_common() is called against a page which is accounted.

mem_cgroup_charge_common() is called when.
 1. a page is added into file cache.
 2. an anon page is _newly_ mapped.

A racy case is that a newly-swapped-in anonymous page is referred from
prural threads in do_swap_page() at the same time.
(a page is not Locked when mem_cgroup_charge() is called from do_swap_page.)

Another case is shmem. It charges its page before calling add_to_page_cache().
Then, mem_cgroup_charge_cache() is called twice. This case is handled in
mem_cgroup_cache_charge(). But this check may be too hacky...

Signed-off-by : KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Cc: David Rientjes <rientjes@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 2008-07-25 01:47:17 -07:00 committed by Linus Torvalds
parent b76734e5e3
commit accf163e6a
1 changed files with 25 additions and 28 deletions
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53
mm/memcontrol.c
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@ -536,28 +536,6 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
if (mem_cgroup_subsys.disabled)
return 0;
/*
* Should page_cgroup's go to their own slab?
* One could optimize the performance of the charging routine
* by saving a bit in the page_flags and using it as a lock
* to see if the cgroup page already has a page_cgroup associated
* with it
*/
retry:
lock_page_cgroup(page);
pc = page_get_page_cgroup(page);
/*
* The page_cgroup exists and
* the page has already been accounted.
*/
if (unlikely(pc)) {
VM_BUG_ON(pc->page != page);
VM_BUG_ON(!pc->mem_cgroup);
unlock_page_cgroup(page);
goto done;
}
unlock_page_cgroup(page);
pc = kmem_cache_alloc(page_cgroup_cache, gfp_mask);
if (unlikely(pc == NULL))
goto err;
@ -618,15 +596,10 @@ retry:
lock_page_cgroup(page);
if (unlikely(page_get_page_cgroup(page))) {
unlock_page_cgroup(page);
/*
* Another charge has been added to this page already.
* We take lock_page_cgroup(page) again and read
* page->cgroup, increment refcnt.... just retry is OK.
*/
res_counter_uncharge(&mem->res, PAGE_SIZE);
css_put(&mem->css);
kmem_cache_free(page_cgroup_cache, pc);
goto retry;
goto done;
}
page_assign_page_cgroup(page, pc);
@ -665,8 +638,32 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
gfp_t gfp_mask)
{
/*
* Corner case handling. This is called from add_to_page_cache()
* in usual. But some FS (shmem) precharges this page before calling it
* and call add_to_page_cache() with GFP_NOWAIT.
*
* For GFP_NOWAIT case, the page may be pre-charged before calling
* add_to_page_cache(). (See shmem.c) check it here and avoid to call
* charge twice. (It works but has to pay a bit larger cost.)
*/
if (!(gfp_mask & __GFP_WAIT)) {
struct page_cgroup *pc;
lock_page_cgroup(page);
pc = page_get_page_cgroup(page);
if (pc) {
VM_BUG_ON(pc->page != page);
VM_BUG_ON(!pc->mem_cgroup);
unlock_page_cgroup(page);
return 0;
}
unlock_page_cgroup(page);
}
if (unlikely(!mm))
mm = &init_mm;
return mem_cgroup_charge_common(page, mm, gfp_mask,
MEM_CGROUP_CHARGE_TYPE_CACHE, NULL);
}