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Message-ID: <1571843149.5937.86.camel@lca.pw>
Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading
 /proc/pagetypeinfo
From:   Qian Cai <cai@lca.pw>
To:     Waiman Long <longman@redhat.com>,
        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>
Date:   Wed, 23 Oct 2019 11:05:49 -0400
In-Reply-To: <a4398f60-c07e-8fa9-c26d-3b8f688e65a1@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>
         <a4398f60-c07e-8fa9-c26d-3b8f688e65a1@redhat.com>
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On Wed, 2019-10-23 at 11:01 -0400, Waiman Long wrote:
> 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.

What are those tools?