Date: Wed, 22 Jul 2015 12:44:21 -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
Message-Id: <20150722124421.3313e8f007d76b386e1d61ec@linux-foundation.org>
In-Reply-To: <20150722162528.GN23374@esperanza>
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	<20150721163500.528bd39bbbc71abc3c8d429b@linux-foundation.org>
	<20150722162528.GN23374@esperanza>
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On Wed, 22 Jul 2015 19:25:28 +0300 Vladimir Davydov <vdavydov@parallels.com> wrote:

> On Tue, Jul 21, 2015 at 04:35:00PM -0700, Andrew Morton wrote:
> > 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...
> 
> I don't understand what you mean by "regular old page scanner". Could
> you please elaborate?

Whenever kswapd or direct reclaim perform an rmap scan, take that as an
opportunity to also update PageIdle().

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