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

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Message-Id: <C448FBC6-60AE-46FA-9548-FF31A22378BC@lca.pw>
Date:   Wed, 23 Oct 2019 08:42:40 -0400
From:   Qian Cai <cai@....pw>
To:     Mel Gorman <mgorman@...e.de>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Waiman Long <longman@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>, 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 Oct 23, 2019, at 5:56 AM, Mel Gorman <mgorman@...e.de> wrote:
> 
> Again, the cost is when reading a proc file. From what Andrew said,
> the lock is necessary to safely walk the list but if anything. I would
> be ok with limiting the length of the walk but honestly, I would also
> be ok with simply deleting the proc file. The utility for debugging a
> problem with it is limited now (it was more important when fragmentation
> avoidance was first introduced) and there is little an admin can do with
> the information. I can't remember the last time I asked for the contents
> of the file when trying to debug a problem. There is a possibility that
> someone will complain but I'm not aware of any utility that reads the
> information and does something useful with it. In the unlikely event
> something breaks, the file can be re-added with a limited walk.

Agree. It is better to remove this file all together in linux-next first for a while to see if anyone complains loudly.