[PATCH v4] memcg: fix leak on wrong LRU with FUSE
From: KAMEZAWA Hiroyuki
Date: Thu Mar 10 2011 - 00:54:54 EST
On Thu, 10 Mar 2011 08:36:59 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> will add. Thank you !
>
Here is v4 based on feedbacks.
==
fs/fuse/dev.c::fuse_try_move_page() does
(1) remove a page by ->steal()
(2) re-add the page to page cache
(3) link the page to LRU if it was not on LRU at (1)
This implies the page is _on_ LRU when it's added to radix-tree.
So, the page is added to memory cgroup while it's on LRU and
the pave will remain in the old(wrong) memcg.
By this bug, force_empty()'s LRU scan cannot find the page and
rmdir() will never ends.
This is the same behavior as SwapCache and needs special care as
- remove page from LRU before overwrite pc->mem_cgroup.
- add page to LRU after overwrite pc->mem_cgroup.
This will fixes memcg's rmdir() hang issue with FUSE.
Changelog v3=v4:
- moved PageLRU() check into the leaf function.
- added comments
Changelog v2=>v3:
- fixed double accounting.
Changelog v1=>v2:
- clean up.
- cover !PageLRU() by pagevec case.
Reviewed-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
mm/memcontrol.c | 70 +++++++++++++++++++++++++++++++++++++++++---------------
1 file changed, 52 insertions(+), 18 deletions(-)
Index: mmotm-0303/mm/memcontrol.c
===================================================================
--- mmotm-0303.orig/mm/memcontrol.c
+++ mmotm-0303/mm/memcontrol.c
@@ -926,18 +926,28 @@ void mem_cgroup_add_lru_list(struct page
}
/*
- * At handling SwapCache, pc->mem_cgroup may be changed while it's linked to
- * lru because the page may.be reused after it's fully uncharged (because of
- * SwapCache behavior).To handle that, unlink page_cgroup from LRU when charge
- * it again. This function is only used to charge SwapCache. It's done under
- * lock_page and expected that zone->lru_lock is never held.
+ * 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_swapcache(struct page *page)
+static void mem_cgroup_lru_del_before_commit(struct page *page)
{
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);
/*
* Forget old LRU when this page_cgroup is *not* used. This Used bit
@@ -948,12 +958,15 @@ static void mem_cgroup_lru_del_before_co
spin_unlock_irqrestore(&zone->lru_lock, flags);
}
-static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
+static void mem_cgroup_lru_add_after_commit(struct page *page)
{
unsigned long flags;
struct zone *zone = page_zone(page);
struct page_cgroup *pc = lookup_page_cgroup(page);
+ /* 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);
/* link when the page is linked to LRU but page_cgroup isn't */
if (PageLRU(page) && !PageCgroupAcctLRU(pc))
@@ -2431,9 +2444,26 @@ static void
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
enum charge_type ctype);
+static void
+__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *mem,
+ enum charge_type ctype)
+{
+ struct page_cgroup *pc = lookup_page_cgroup(page);
+ /*
+ * 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);
+ __mem_cgroup_commit_charge(mem, page, 1, pc, ctype);
+ mem_cgroup_lru_add_after_commit(page);
+ return;
+}
+
int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
gfp_t gfp_mask)
{
+ struct mem_cgroup *mem = NULL;
int ret;
if (mem_cgroup_disabled())
@@ -2468,14 +2498,22 @@ int mem_cgroup_cache_charge(struct page
if (unlikely(!mm))
mm = &init_mm;
- if (page_is_file_cache(page))
- return mem_cgroup_charge_common(page, mm, gfp_mask,
- MEM_CGROUP_CHARGE_TYPE_CACHE);
+ if (page_is_file_cache(page)) {
+ ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, &mem, true);
+ if (ret || !mem)
+ return ret;
+ /*
+ * FUSE reuses pages without going through the final
+ * put that would remove them from the LRU list, make
+ * sure that they get relinked properly.
+ */
+ __mem_cgroup_commit_charge_lrucare(page, mem,
+ MEM_CGROUP_CHARGE_TYPE_CACHE);
+ return ret;
+ }
/* shmem */
if (PageSwapCache(page)) {
- struct mem_cgroup *mem;
-
ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &mem);
if (!ret)
__mem_cgroup_commit_charge_swapin(page, mem,
@@ -2532,17 +2570,13 @@ static void
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
enum charge_type ctype)
{
- struct page_cgroup *pc;
-
if (mem_cgroup_disabled())
return;
if (!ptr)
return;
cgroup_exclude_rmdir(&ptr->css);
- pc = lookup_page_cgroup(page);
- mem_cgroup_lru_del_before_commit_swapcache(page);
- __mem_cgroup_commit_charge(ptr, page, 1, pc, ctype);
- mem_cgroup_lru_add_after_commit_swapcache(page);
+
+ __mem_cgroup_commit_charge_lrucare(page, ptr, ctype);
/*
* Now swap is on-memory. This means this page may be
* counted both as mem and swap....double count.
--
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