LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Michal Hocko <mhocko@suse.cz>
To: Christoph Lameter <cl@linux.com>
Cc: Vinayak Menon <vinmenon@codeaurora.org>,
	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: Tue, 27 Jan 2015 11:52:42 +0100	[thread overview]
Message-ID: <20150127105242.GC19880@dhcp22.suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.11.1501261233550.16786@gentwo.org>

On Mon 26-01-15 12:35:00, Christoph Lameter wrote:
> On Mon, 26 Jan 2015, Michal Hocko wrote:
> 
> > > Please do not run the vmstat_updates concurrently. They update shared
> > > cachelines and therefore can cause bouncing cachelines if run concurrently
> > > on multiple cpus.
> >
> > Would you preffer to call smp_call_function_single on each CPU
> > which needs an update? That would make vmstat_shepherd slower but that
> > is not a big deal, is it?
> 
> Run it from the timer interrupt as usual from a work request? Those are
> staggered.

I am not following. The idea was to run vmstat_shepherd in a kernel
thread and waking up as per defined timeout and then check need_update
for each CPU and call smp_call_function_single to refresh the timer
rather than building a mask and then calling sm_call_function_many to
reduce paralel contention on the shared counters.

> > Anyway I am wondering whether the cache line bouncing between
> > vmstat_update instances is a big deal in the real life. Updating shared
> > counters whould bounce with many CPUs but this is an operation which is
> > not done often. Also all the CPUs would have update the same counters
> > all the time and I am not sure this happens that often. Do you have a
> > load where this would be measurable?
> 
> Concurrent page faults update lots of counters concurrently.

True

> But will those trigger the smp_call_function?

The smp_call_function was meant to be called only from the
vmstat_shepherd context which does happen "rarely". Or am I missing your
point here?

-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2015-01-27 10:52 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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20150127105242.GC19880@dhcp22.suse.cz \
    --to=mhocko@suse.cz \
    --cc=akpm@linux-foundation.org \
    --cc=cl@linux.com \
    --cc=hannes@cmpxchg.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mgorman@suse.de \
    --cc=minchan@kernel.org \
    --cc=vdavydov@parallels.com \
    --cc=vinmenon@codeaurora.org \
    --subject='Re: [PATCH v2] mm: vmscan: fix the page state calculation in too_many_isolated' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).