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Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading
 /proc/pagetypeinfo
To:     Qian Cai <cai@lca.pw>, Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>, Roman Gushchin <guro@fb.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Jann Horn <jannh@google.com>, Song Liu <songliubraving@fb.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rafael Aquini <aquini@redhat.com>
References: <20191022162156.17316-1-longman@redhat.com>
 <20191022145902.d9c4a719c0b32175e06e4eee@linux-foundation.org>
 <2236495a-ead0-e08e-3fb6-f3ab906b75b6@redhat.com>
 <1571842093.5937.84.camel@lca.pw>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <a4398f60-c07e-8fa9-c26d-3b8f688e65a1@redhat.com>
Date:   Wed, 23 Oct 2019 11:01:04 -0400
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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 wil=
l 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