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Date:   Thu, 24 Oct 2019 11:33:13 +0800
From:   Feng Tang <feng.tang@intel.com>
To:     Waiman Long <longman@redhat.com>
Cc:     Qian Cai <cai@lca.pw>, Andrew Morton <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.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>
Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading
 /proc/pagetypeinfo
Message-ID: <20191024033313.GA42124@shbuild999.sh.intel.com>
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On Wed, Oct 23, 2019 at 11:01:04PM +0800, 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.

We have been using the /proc/pagetypeinfo for debugging, mainly for
client platforms like phones/tablets. We met problems like very slow
system response or OOM things, and many of them could be related with
memory pressure or fragmentation issues, where monitoring /proc/pagetypeinfo
will be very useful for debugging.

So I think Michal's idea to change it to 0400 is a good idea.

Thanks,
Feng

 
> Cheers,
> Longman
> 
>