linux-kernel - Re: [PATCH V5 6/6] proc: show MADV

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Message-Id: <20170303161027.6fe4ceb0bcd27e1dbed44a5d@linux-foundation.org>
Date:   Fri, 3 Mar 2017 16:10:27 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Johannes Weiner <hannes@...xchg.org>, Shaohua Li <shli@...com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Kernel-team@...com, minchan@...nel.org, hughd@...gle.com,
        riel@...hat.com, mgorman@...hsingularity.net
Subject: Re: [PATCH V5 6/6] proc: show MADV_FREE pages info in smaps

On Thu, 2 Mar 2017 17:30:54 +0100 Michal Hocko <mhocko@...nel.org> wrote:

> > It's not that I think you're wrong: it *is* an implementation detail.
> > But we take a bit of incoherency from batching all over the place, so
> > it's a little odd to take a stand over this particular instance of it
> > - whether demanding that it'd be fixed, or be documented, which would
> > only suggest to users that this is special when it really isn't etc.
> 
> I am not aware of other counter printed in smaps that would suffer from
> the same problem, but I haven't checked too deeply so I might be wrong. 
> 
> Anyway it seems that I am alone in my position so I will not insist.
> If we have any bug report then we can still fix it.

A single lru_add_drain_all() right at the top level (in smaps_show()?)
won't kill us and should significantly improve this issue.  And it
might accidentally make some of the other smaps statistics more
accurate as well.

If not, can we please have a nice comment somewhere appropriate which
explains why LazyFree is inaccurate and why we chose to leave it that
way?