path: root/mm
diff options
authorJohannes Weiner <hannes@cmpxchg.org>2011-02-01 15:52:43 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-02-02 16:03:19 -0800
commit19942822df65ee4a47c2e6d6d70cace1b7f01710 (patch)
tree1fe6fdcc92ae7e64014c04676fc91e0105bdf344 /mm
parent9221edb7120e2dc3ae90f1c58514979f7ba40e46 (diff)
memcg: prevent endless loop when charging huge pages to near-limit group
If reclaim after a failed charging was unsuccessful, the limits are checked again, just in case they settled by means of other tasks. This is all fine as long as every charge is of size PAGE_SIZE, because in that case, being below the limit means having at least PAGE_SIZE bytes available. But with transparent huge pages, we may end up in an endless loop where charging and reclaim fail, but we keep going because the limits are not yet exceeded, although not allowing for a huge page. Fix this up by explicitely checking for enough room, not just whether we are within limits. Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Cc: Balbir Singh <balbir@linux.vnet.ibm.com> Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 28 insertions, 7 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 50eb50e100fd..0e81eb5f0aea 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1111,6 +1111,23 @@ static bool mem_cgroup_check_under_limit(struct mem_cgroup *mem)
return false;
+ * mem_cgroup_check_margin - check if the memory cgroup allows charging
+ * @mem: memory cgroup to check
+ * @bytes: the number of bytes the caller intends to charge
+ *
+ * Returns a boolean value on whether @mem can be charged @bytes or
+ * whether this would exceed the limit.
+ */
+static bool mem_cgroup_check_margin(struct mem_cgroup *mem, unsigned long bytes)
+ if (!res_counter_check_margin(&mem->res, bytes))
+ return false;
+ if (do_swap_account && !res_counter_check_margin(&mem->memsw, bytes))
+ return false;
+ return true;
static unsigned int get_swappiness(struct mem_cgroup *memcg)
struct cgroup *cgrp = memcg->css.cgroup;
@@ -1852,15 +1869,19 @@ static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
- gfp_mask, flags);
+ gfp_mask, flags);
+ if (mem_cgroup_check_margin(mem_over_limit, csize))
+ return CHARGE_RETRY;
- * try_to_free_mem_cgroup_pages() might not give us a full
- * picture of reclaim. Some pages are reclaimed and might be
- * moved to swap cache or just unmapped from the cgroup.
- * Check the limit again to see if the reclaim reduced the
- * current usage of the cgroup before giving up
+ * Even though the limit is exceeded at this point, reclaim
+ * may have been able to free some pages. Retry the charge
+ * before killing the task.
+ *
+ * Only for regular pages, though: huge pages are rather
+ * unlikely to succeed so close to the limit, and we fall back
+ * to regular pages anyway in case of failure.
- if (ret || mem_cgroup_check_under_limit(mem_over_limit))
+ if (csize == PAGE_SIZE && ret)