linux-kernel - Re: [PATCH] mm/vmstat: retrieve more accurate vmstat value

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Message-ID: <20151125180350.GT27283@dhcp22.suse.cz>
Date:	Wed, 25 Nov 2015 19:03:50 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/vmstat: retrieve more accurate vmstat value

On Wed 25-11-15 10:04:44, Christoph Lameter wrote:
> On Wed, 25 Nov 2015, Joonsoo Kim wrote:
> 
> > I think that maintaining duplicate counter to guarantee accuracy isn't
> > reasonable solution. It would cause more overhead to the system.
> 
> Simply remove the counter from the vmstat handling and do it differently
> then.

We definitely do not want yet another set of counters. vmstat counters
are not only to be exported into the userspace. We have in kernel users
as well. I do agree that there are users who can cope with some level of
imprecision though and those which depend on the accuracy can use
zone_page_state_snapshot which doesn't impose any overhead on others.
[...]
-- 
Michal Hocko
SUSE Labs
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