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Message-ID: <CA+55aFyVqdk0p6pmEx_gOs_AiH0TJ23ZEUDZHc9kiFbqEk8UOw@mail.gmail.com>
Date: Thu, 11 Aug 2016 09:55:33 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Christoph Hellwig <hch@....de>
Cc: "Huang, Ying" <ying.huang@...el.com>,
Dave Chinner <david@...morbit.com>,
LKML <linux-kernel@...r.kernel.org>,
Bob Peterson <rpeterso@...hat.com>,
Wu Fengguang <fengguang.wu@...el.com>, LKP <lkp@...org>
Subject: Re: [LKP] [lkp] [xfs] 68a9f5e700: aim7.jobs-per-min -13.6% regression
On Thu, Aug 11, 2016 at 8:57 AM, Christoph Hellwig <hch@....de> wrote:
>
> The one liner below (not tested yet) to simply remove it should fix that
> up. I also noticed we have a spurious pagefault_disable/enable, I
> need to dig into the history of that first, though.
Hopefully the pagefault_disable/enable doesn't matter for this case.
Can we get this one-liner tested with the kernel robot for comparison?
I really think a messed-up LRU list could cause bad IO patterns, and
end up keeping dirty pages around that should be streaming out to disk
and re-used, so causing memory pressure etc for no good reason.
I think the mapping->tree_lock issue that Dave sees is interesting
too, but the kswapd activity (and the extra locking it causes) could
also be a symptom of the same thing - memory pressure due to just
putting pages in the active file that simply shouldn't be there.
So the trivial oneliner _might_ just explain things. It would be
really nice if the regression turns out to be due to something so
easily fixed.
Linus
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