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authorFeng Tang <feng.tang@intel.com>2020-06-04 16:46:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-04 19:06:20 -0700
commitc571686a92ffd30d9f6092ce3f697e125bf96fd5 (patch)
tree8d15e8f73fc9e83f3889e93d9385e5d2c4415130 /arch/h8300
parent76e278d6b50534092038d4117d7a2687af034107 (diff)
mm/util.c: remove the VM_WARN_ONCE for vm_committed_as underflow check
This check was added by commit 82f71ae4a2b8 ("mm: catch memory commitment underflow") in 2014 to have a safety check for issues which have been fixed. And there has been few report caught by it, as described in its commit log: : This shouldn't happen any more - the previous two patches fixed : the committed_as underflow issues. But it was really found by Qian Cai when he used the LTP memory stress suite to test a RFC patchset, which tries to improve scalability of per-cpu counter 'vm_committed_as', by chosing a bigger 'batch' number for loose overcommit policies (OVERCOMMIT_ALWAYS and OVERCOMMIT_GUESS), while keeping current number for OVERCOMMIT_NEVER. With that patchset, when system firstly uses a loose policy, the 'vm_committed_as' count could be a big negative value, as its big 'batch' number allows a big deviation, then when the policy is changed to OVERCOMMIT_NEVER, the 'batch' will be decreased to a much smaller value, thus hits this WARN check. To mitigate this, one proposed solution is to queue work on all online CPUs to do a local sync for 'vm_committed_as' when changing policy to OVERCOMMIT_NEVER, plus some global syncing to garante the case won't be hit. But this solution is costy and slow, given this check hasn't shown real trouble or benefit, simply drop it from one hot path of MM. And perf stats does show some tiny saving for removing it. Reported-by: Qian Cai <cai@lca.pw> Signed-off-by: Feng Tang <feng.tang@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Qian Cai <cai@lca.pw> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Andi Kleen <andi.kleen@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Kees Cook <keescook@chromium.org> Link: http://lkml.kernel.org/r/20200603094804.GB89848@shbuild999.sh.intel.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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