[PATCH] memcg: fix to leave pages on wrong LRU with FUSE.

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

At this point, I'm not sure this is a fix for 
   https://bugzilla.kernel.org/show_bug.cgi?id=30432.

The behavior seems very similar to SwapCache case and this is a possible
bug and this patch can be a fix. Nishimura-san, how do you think ?

But I'm not sure how to test this....please review.

=
fs/fuse/dev.c::fuse_try_move_page() does

   (1) remove a page from page cache 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 can be _on_ LRU when add_to_page_cache_locked() is called.
So, the page is added to a memory cgroup while it's on LRU.

This is the same behavior as SwapCache, 'newly charged pages may be on LRU'
and needs special care as
 - remove page from old memcg's LRU before overwrite pc->mem_cgroup.
 - add page to new memcg's LRU after overwrite pc->mem_cgroup.

So, reusing SwapCache code with renaming for fix.

Note: a page on pagevec(LRU).

If a page is not PageLRU(page) but on pagevec(LRU), it may be added to LRU
while we overwrite page->mapping. But in that case, PCG_USED bit of
the page_cgroup is not set and the page_cgroup will not be added to
wrong memcg's LRU. So, this patch's logic will work fine.
(It has been tested with SwapCache.)

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/memcontrol.c |   42 +++++++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 19 deletions(-)

Index: mmotm-0303/mm/memcontrol.c
===================================================================
--- mmotm-0303.orig/mm/memcontrol.c
+++ mmotm-0303/mm/memcontrol.c
@@ -926,13 +926,12 @@ 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);
@@ -948,7 +947,7 @@ 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);
@@ -2428,7 +2427,7 @@ int mem_cgroup_newpage_charge(struct pag
 }
 
 static void
-__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
+__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *ptr,
 					enum charge_type ctype);
 
 int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
@@ -2468,17 +2467,22 @@ 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,
+	if (page_is_file_cache(page) && !PageLRU(page)) {
+		ret = mem_cgroup_charge_common(page, mm, gfp_mask,
 				MEM_CGROUP_CHARGE_TYPE_CACHE);
-
-	/* shmem */
-	if (PageSwapCache(page)) {
+	} else if (page_is_file_cache(page)) {
+		struct mem_cgroup *mem;
+		/* Page on LRU should be moved to the _new_ LRU */
+		ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, &mem, true);
+		if (!ret)
+			__mem_cgroup_commit_charge_lrucare(page, mem,
+					MEM_CGROUP_CHARGE_TYPE_CACHE);
+	} else 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,
+			__mem_cgroup_commit_charge_lrucare(page, mem,
 					MEM_CGROUP_CHARGE_TYPE_SHMEM);
 	} else
 		ret = mem_cgroup_charge_common(page, mm, gfp_mask,
@@ -2529,7 +2533,7 @@ charge_cur_mm:
 }
 
 static void
-__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
+__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *ptr,
 					enum charge_type ctype)
 {
 	struct page_cgroup *pc;
@@ -2540,9 +2544,9 @@ __mem_cgroup_commit_charge_swapin(struct
 		return;
 	cgroup_exclude_rmdir(&ptr->css);
 	pc = lookup_page_cgroup(page);
-	mem_cgroup_lru_del_before_commit_swapcache(page);
+	mem_cgroup_lru_del_before_commit(page);
 	__mem_cgroup_commit_charge(ptr, page, 1, pc, ctype);
-	mem_cgroup_lru_add_after_commit_swapcache(page);
+	mem_cgroup_lru_add_after_commit(page);
 	/*
 	 * Now swap is on-memory. This means this page may be
 	 * counted both as mem and swap....double count.
@@ -2580,7 +2584,7 @@ __mem_cgroup_commit_charge_swapin(struct
 
 void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
 {
-	__mem_cgroup_commit_charge_swapin(page, ptr,
+	__mem_cgroup_commit_charge_lrucare(page, ptr,
 					MEM_CGROUP_CHARGE_TYPE_MAPPED);
 }
 

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