linux-kernel - Re: [PATCH V2 5/7] mm: add vmstat account for MADV

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Message-ID: <20170221094353.GG15595@dhcp22.suse.cz>
Date:   Tue, 21 Feb 2017 10:43:54 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Shaohua Li <shli@...com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Kernel-team@...com, danielmicay@...il.com, minchan@...nel.org,
        hughd@...gle.com, hannes@...xchg.org, riel@...hat.com,
        mgorman@...hsingularity.net, akpm@...ux-foundation.org
Subject: Re: [PATCH V2 5/7] mm: add vmstat account for MADV_FREE pages

[Sorry for a late reply I was on vacation last week]

On Fri 10-02-17 09:50:15, Shaohua Li wrote:
> On Fri, Feb 10, 2017 at 02:27:27PM +0100, Michal Hocko wrote:
> > On Fri 03-02-17 15:33:21, Shaohua Li wrote:
> > > Show MADV_FREE pages info in proc/sysfs files.
> > 
> > How are we going to use this information? Why it isn't sufficient to
> > watch for lazyfree events? I mean this adds quite some code and it is
> > not clear (at least from the changelog) we we need this information.
> 
> It's just like any other meminfo we added to let user know what happens in the
> system. Users can use the info for monitoring/diagnosing. the
> lazyfree/lazyfreed events can't reflect the lazyfree page info because
> 'lazyfree - lazyfreed' doesn't equal current lazyfree pages and the events
> aren't per-node. I'll add more description in the changelog.

Well, I would prefer to not add new counters until there is a strong
reason for them. Maybe a trace point would be more appropriate for
debugging purposes.
-- 
Michal Hocko
SUSE Labs