Date: Tue, 21 Jul 2015 16:35:00 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Vladimir Davydov <vdavydov@parallels.com>
Cc: Andres Lagar-Cavilla <andreslc@google.com>,
        Minchan Kim <minchan@kernel.org>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>,
        Greg Thelen <gthelen@google.com>,
        Michel Lespinasse <walken@google.com>,
        David Rientjes <rientjes@google.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        Jonathan Corbet <corbet@lwn.net>, <linux-api@vger.kernel.org>,
        <linux-doc@vger.kernel.org>, <linux-mm@kvack.org>,
        <cgroups@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -mm v9 7/8] proc: export idle flag via kpageflags
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On Sun, 19 Jul 2015 15:31:16 +0300 Vladimir Davydov <vdavydov@parallels.com> wrote:

> As noted by Minchan, a benefit of reading idle flag from
> /proc/kpageflags is that one can easily filter dirty and/or unevictable
> pages while estimating the size of unused memory.
> 
> Note that idle flag read from /proc/kpageflags may be stale in case the
> page was accessed via a PTE, because it would be too costly to iterate
> over all page mappings on each /proc/kpageflags read to provide an
> up-to-date value. To make sure the flag is up-to-date one has to read
> /proc/kpageidle first.

Is there any value in teaching the regular old page scanner to update
these flags?  If it's doing an rmap scan anyway...

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