Date: Wed, 22 Jul 2015 19:25:28 +0300
From: Vladimir Davydov <vdavydov@parallels.com>
To: Andrew Morton <akpm@linux-foundation.org>
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: <20150722162528.GN23374@esperanza>
References: <cover.1437303956.git.vdavydov@parallels.com>
 <4c1eb396150ee14d7c3abf1a6f36ec8cc9dd9435.1437303956.git.vdavydov@parallels.com>
 <20150721163500.528bd39bbbc71abc3c8d429b@linux-foundation.org>
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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?

Thanks,
Vladimir
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