The patch titled
memcg: remove a redundant check
has been removed from the -mm tree. Its filename was
memcg-remove-a-redundant-check.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: memcg: remove a redundant check
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxx>
Cc: Li Zefan <lizf@xxxxxxxxxxxxxx>
Cc: Hugh Dickins <hugh@xxxxxxxxxxx>
Cc: YAMAMOTO Takashi <yamamoto@xxxxxxxxxxxxx>
Cc: Paul Menage <menage@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 53 +++++++++++++++++++++-------------------------
1 file changed, 25 insertions(+), 28 deletions(-)
diff -puN mm/memcontrol.c~memcg-remove-a-redundant-check mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-remove-a-redundant-check
+++ a/mm/memcontrol.c
@@ -536,28 +536,6 @@ static int mem_cgroup_charge_common(stru
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,
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);
}
_
Patches currently in -mm which might be from kamezawa.hiroyu@xxxxxxxxxxxxxx are
origin.patch
memrlimit-add-memrlimit-controller-documentation.patch
memrlimit-setup-the-memrlimit-controller.patch
memrlimit-cgroup-mm-owner-callback-changes-to-add-task-info.patch
memrlimit-add-memrlimit-controller-accounting-and-control.patch
memrlimit-improve-error-handling.patch
memrlimit-improve-error-handling-update.patch
memrlimit-handle-attach_task-failure-add-can_attach-callback.patch
mm-speculative-page-references-fix-migration_entry_wait-for-speculative-page-cache.patch
define-page_file_cache-function-fix-splitlru-shmem_getpage-setpageswapbacked-sooner.patch
vmscan-split-lru-lists-into-anon-file-sets-splitlru-memcg-swapbacked-pages-active.patch
vmscan-second-chance-replacement-for-anonymous-pages-fix.patch
vmscan-second-chance-replacement-for-anonymous-pages-memcg-lru-scan-fix.patch
unevictable-lru-infrastructure-putback_lru_page-unevictable-page-handling-rework.patch
mlock-mlocked-pages-are-unevictable-fix-truncate-race-and-sevaral-comments.patch
fix-double-unlock_page-in-2626-rc5-mm3-kernel-bug-at-mm-filemapc-575.patch
restore-patch-failure-of-vmstat-unevictable-and-mlocked-pages-vm-eventspatch.patch
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