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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 04ded27..5b3759b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -536,28 +536,6 @@
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 @@
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_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);
}