The patch titled Subject: mm/memcg: fix refcount error while moving and swapping has been added to the -mm tree. Its filename is mm-memcg-fix-refcount-error-while-moving-and-swapping.patch

This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-memcg-fix-refcount-error-while-m... and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-memcg-fix-refcount-error-while-m...

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------------------------------------------------------ From: Hugh Dickins hughd@google.com Subject: mm/memcg: fix refcount error while moving and swapping

It was hard to keep a test running, moving tasks between memcgs with move_charge_at_immigrate, while swapping: mem_cgroup_id_get_many()'s refcount is discovered to be 0 (supposedly impossible), so it is then forced to REFCOUNT_SATURATED, and after thousands of warnings in quick succession, the test is at last put out of misery by being OOM killed.

This is because of the way moved_swap accounting was saved up until the task move gets completed in __mem_cgroup_clear_mc(), deferred from when mem_cgroup_move_swap_account() actually exchanged old and new ids. Concurrent activity can free up swap quicker than the task is scanned, bringing id refcount down 0 (which should only be possible when offlining).

Just skip that optimization: do that part of the accounting immediately.

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2007071431050.4726@eggly.anvils Fixes: 615d66c37c75 ("mm: memcontrol: fix memcg id ref counter on swap charge move") Signed-off-by: Hugh Dickins hughd@google.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Alex Shi alex.shi@linux.alibaba.com Cc: Shakeel Butt shakeelb@google.com Cc: Michal Hocko mhocko@suse.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memcontrol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/memcontrol.c~mm-memcg-fix-refcount-error-while-moving-and-swapping +++ a/mm/memcontrol.c @@ -5669,7 +5669,6 @@ static void __mem_cgroup_clear_mc(void) if (!mem_cgroup_is_root(mc.to)) page_counter_uncharge(&mc.to->memory, mc.moved_swap);

- mem_cgroup_id_get_many(mc.to, mc.moved_swap); css_put_many(&mc.to->css, mc.moved_swap);

mc.moved_swap = 0; @@ -5860,7 +5859,8 @@ put: /* get_mctgt_type() gets the page ent = target.ent; if (!mem_cgroup_move_swap_account(ent, mc.from, mc.to)) { mc.precharge--; - /* we fixup refcnts and charges later. */ + mem_cgroup_id_get_many(mc.to, 1); + /* we fixup other refcnts and charges later. */ mc.moved_swap++; } break; _

Patches currently in -mm which might be from hughd@google.com are

mm-memcg-fix-refcount-error-while-moving-and-swapping.patch