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From: Michal Hocko <mhocko@suse.cz>
To: Vinayak Menon <vinmenon@codeaurora.org>
Cc: Christoph Lameter <cl@linux.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	akpm@linux-foundation.org, hannes@cmpxchg.org,
	vdavydov@parallels.com, mgorman@suse.de, minchan@kernel.org
Subject: Re: [PATCH v2] mm: vmscan: fix the page state calculation in too_many_isolated
Date: Wed, 21 Jan 2015 15:39:20 +0100	[thread overview]
Message-ID: <20150121143920.GD23700@dhcp22.suse.cz> (raw)
In-Reply-To: <54BC879C.90505@codeaurora.org>

On Mon 19-01-15 09:57:08, Vinayak Menon wrote:
> On 01/18/2015 01:18 AM, Christoph Lameter wrote:
> >On Sat, 17 Jan 2015, Vinayak Menon wrote:
> >
> >>which had not updated the vmstat_diff. This CPU was in idle for around 30
> >>secs. When I looked at the tvec base for this CPU, the timer associated with
> >>vmstat_update had its expiry time less than current jiffies. This timer had
> >>its deferrable flag set, and was tied to the next non-deferrable timer in the
> >
> >We can remove the deferrrable flag now since the vmstat threads are only
> >activated as necessary with the recent changes. Looks like this could fix
> >your issue?
> >
> 
> Yes, this should fix my issue.

Does it? Because I would prefer not getting into un-synced state much
more than playing around one specific place which shows the problems
right now.

> But I think we may need the fix in too_many_isolated, since there can still
> be a delay of few seconds (HZ by default and even more because of reasons
> pointed out by Michal) which will result in reclaimers unnecessarily
> entering congestion_wait. No ?

I think we can solve this as well. We can stick vmstat_shepherd into a
kernel thread with a loop with the configured timeout and then create a
mask of CPUs which need the update and run vmstat_update from
IPI context (smp_call_function_many).
We would have to drop cond_resched from refresh_cpu_vm_stats of
course. The nr_zones x NR_VM_ZONE_STAT_ITEMS in the IPI context
shouldn't be excessive but I haven't measured that so I might be easily
wrong.

Anyway, that should work more reliably than the current scheme and
should help to reduce pointless wakeups which the original patchset was
addressing.  Or am I missing something?

-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2015-01-21 14:39 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-14 11:36 Vinayak Menon
2015-01-14 16:50 ` Michal Hocko
2015-01-15 17:24   ` Vinayak Menon
2015-01-16 15:49     ` Michal Hocko
2015-01-16 17:57       ` Michal Hocko
2015-01-16 19:17         ` Christoph Lameter
2015-01-17 15:18       ` Vinayak Menon
2015-01-17 19:48         ` Christoph Lameter
2015-01-19  4:27           ` Vinayak Menon
2015-01-21 14:39             ` Michal Hocko [this message]
2015-01-22 15:16               ` Vlastimil Babka
2015-01-22 16:11               ` Christoph Lameter
2015-01-26 17:46                 ` Michal Hocko
2015-01-26 18:35                   ` Christoph Lameter
2015-01-27 10:52                     ` Michal Hocko
2015-01-27 16:59                       ` Christoph Lameter
2015-01-30 15:28                         ` Michal Hocko
2015-01-26 17:28           ` Michal Hocko
2015-01-26 18:35             ` Christoph Lameter
2015-01-26 22:11             ` Andrew Morton
2015-01-27 10:41               ` Michal Hocko
2015-01-27 10:33             ` Vinayak Menon
2015-01-27 10:45               ` Michal Hocko
2015-01-29 17:32       ` Christoph Lameter
2015-01-30 15:27         ` Michal Hocko
2015-01-16  1:17 ` Andrew Morton
2015-01-16  5:10   ` Vinayak Menon
2015-01-17 16:29   ` Vinayak Menon
2015-02-11 22:14     ` Andrew Morton
2015-02-12 16:19       ` Vlastimil Babka

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