mm: update_lru_size warn and reset bad lru_size
authorHugh Dickins <hughd@google.com>
Fri, 20 May 2016 00:12:35 +0000 (17:12 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 20 May 2016 02:12:14 +0000 (19:12 -0700)
commitca707239e8a7958ffb1c31737d41cae1a674c938
tree37792a1ea8ed942fe0337ffa03ef9bb34329a881
parent1269019e69a6798db15edea8921f83215ef954d6
mm: update_lru_size warn and reset bad lru_size

Though debug kernels have a VM_BUG_ON to help protect from misaccounting
lru_size, non-debug kernels are liable to wrap it around: and then the
vast unsigned long size draws page reclaim into a loop of repeatedly
doing nothing on an empty list, without even a cond_resched().

That soft lockup looks confusingly like an over-busy reclaim scenario,
with lots of contention on the lru_lock in shrink_inactive_list(): yet
has a totally different origin.

Help differentiate with a custom warning in
mem_cgroup_update_lru_size(), even in non-debug kernels; and reset the
size to avoid the lockup.  But the particular bug which suggested this
change was mine alone, and since fixed.

Make it a WARN_ONCE: the first occurrence is the most informative, a
flurry may follow, yet even when rate-limited little more is learnt.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Yang Shi <yang.shi@linaro.org>
Cc: Ning Qu <quning@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
include/linux/mm_inline.h
mm/memcontrol.c