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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo
Date:   Wed, 23 Oct 2019 08:42:40 -0400
Message-Id: <C448FBC6-60AE-46FA-9548-FF31A22378BC@lca.pw>
References: <20191023095607.GE3016@techsingularity.net>
Cc:     Michal Hocko <mhocko@kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Waiman Long <longman@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Johannes Weiner <hannes@cmpxchg.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>
In-Reply-To: <20191023095607.GE3016@techsingularity.net>
To:     Mel Gorman <mgorman@suse.de>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Oct 23, 2019, at 5:56 AM, Mel Gorman <mgorman@suse.de> wrote:
>=20
> Again, the cost is when reading a proc file. =46rom 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.=