[RFC][BUGFIX][PATCH 1/2] transhuge-memcg: fix for memcg compound

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

We should increase/decrease css->refcnt properly in charging/uncharging compound pages.

Without this patch, a bug like below happens:

1. create a memcg directory.
2. run a program which uses enough memory to allocate them as transparent huge pages.
3. kill the program.
4. try to remove the directory, which will never finish.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b1ac9b1..b74bd83 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1650,8 +1650,9 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
 	}
 	if (csize > page_size)
 		refill_stock(mem, csize - page_size);
+	/* increase css->refcnt by the number of tail pages */
 	if (page_size != PAGE_SIZE)
-		__css_get(&mem->css, page_size);
+		__css_get(&mem->css, (page_size >> PAGE_SHIFT) - 1);
 done:
 	return 0;
 nomem:
@@ -2237,7 +2238,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 	memcg_check_events(mem, page);
 	/* at swapout, this memcg will be accessed to record to swap */
 	if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
-		css_put(&mem->css);
+		__css_put(&mem->css, page_size >> PAGE_SHIFT);
 
 	return mem;
 

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