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Commit accf163e authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
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memcg: remove a redundant check 



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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b76734e5

mm/memcontrol.c

+25 −28
Original line number Diff line number Diff line
@@ -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 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm, 
	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);

}