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From: Johannes Weiner <hannes@cmpxchg.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, mhocko@suse.com, vdavydov.dev@gmail.com
Subject: Re: [patch 07/15] mm: memcontrol: fix excessive complexity in memory.stat reporting
Date: Fri, 12 Jan 2018 12:05:01 -0500	[thread overview]
Message-ID: <20180112170501.GA10320@cmpxchg.org> (raw)
In-Reply-To: <20171206170635.e3e45c895750538ee9283033@linux-foundation.org>

Sorry, this email slipped through the cracks.

On Wed, Dec 06, 2017 at 05:06:35PM -0800, Andrew Morton wrote:
> On Fri, 1 Dec 2017 13:57:50 +0000 Johannes Weiner <hannes@cmpxchg.org> wrote:
> 
> > The memcg cpu_dead callback can be called early during startup
> > (CONFIG_DEBUG_HOTPLUG_CPU0) with preemption enabled, which triggers a
> > warning in its __this_cpu_xchg() calls. But CPU locality is always
> > guaranteed, which is the only thing we really care about here.
> > 
> > Using the preemption-safe this_cpu_xchg() addresses this problem.
> > 
> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> > ---
> > 
> > Andrew, can you please merge this fixlet into the original patch?
> 
> Did.
> 
> I see that lkp-robot identified a performance regression and pointed
> the finger at this patch?

Right, it reports a perf drop in page fault stress tests, but that is
to be the expected trade-off. Before, we'd do everything per cpu, and
have to collapse all counters everytime somebody would read the stats.
Now we fold them in batches, which introduces a periodic atomic when
the batches are flushed (same frequency as we per-cpu cache charges
for the atomic page_counter).

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      reply	other threads:[~2018-01-12 17:04 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-30 22:15 akpm
2017-12-01 13:57 ` Johannes Weiner
2017-12-07  1:06   ` Andrew Morton
2018-01-12 17:05     ` Johannes Weiner [this message]

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