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

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Message-ID: <a4398f60-c07e-8fa9-c26d-3b8f688e65a1@redhat.com>
Date:   Wed, 23 Oct 2019 11:01:04 -0400
From:   Waiman Long <longman@...hat.com>
To:     Qian Cai <cai@....pw>, Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.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 10/23/19 10:48 AM, Qian Cai wrote:
>>> this still isn't a bulletproof fix.  Maybe just terminate the list
>>> walk if freecount reaches 1024.  Would anyone really care?
>>>
>>> Sigh.  I wonder if anyone really uses this thing for anything
>>> important.  Can we just remove it all?
>>>
>> Removing it will be a breakage of kernel API.
> Who cares about breaking this part of the API that essentially nobody will use
> this file?
>
There are certainly tools that use /proc/pagetypeinfo and this is how
the problem is found. I am not against removing it, but we have to be
careful and deprecate it in way that minimize user impact.

Cheers,
Longman