linux-kernel - Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo

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Message-ID: <20191024133859.GX17610@dhcp22.suse.cz>
Date:   Thu, 24 Oct 2019 15:38:59 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Qian Cai <cai@....pw>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Waiman Long <longman@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Jann Horn <jannh@...gle.com>, Song Liu <songliubraving@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading
 /proc/pagetypeinfo

On Thu 24-10-19 07:11:52, Qian Cai wrote:
> 
> 
> > On Oct 24, 2019, at 3:42 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > 
> > It's been useful for debugging memory fragmentation problems and we do
> > not have anything that would provide a similar information. Considering
> 
> Actually, zoneinfo and buddyinfo are somewhat similar to it. Why
> the extra information in pagetypeinfo is still useful in debugging
> today’s real-world scenarios?

Because the migrate type is the information that helps to understand
fragmentation related issues. I am pretty sure Vlastimil would tell you
much more.

> > that making it root only is trivial and reducing the lock hold times
> > likewise I do not really see any strong reason to dump it at this
> > moment.
> 
> There is no need to hurry this, and clearly this is rather a good
> opportunity to discuss the consolidation of memory fragmentation
> debugging to ease the maintenance in long term.

Right. I think we should address the issue at hands first and then
handle any possible consolidations.

-- 
Michal Hocko
SUSE Labs