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Date: Mon, 5 Nov 2012 15:54:43 -0800
From: Arun Sharma <asharma@fb.com>
Subject: Re: [RFC v2] Support volatile range for anon vma
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To: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Paul Turner <pjt@google.com>, Andrew Morton <akpm@linux-foundation.org>, Minchan Kim <minchan@kernel.org>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, John Stultz <john.stultz@linaro.org>, Christoph Lameter <cl@linux.com>, Android Kernel Team <kernel-team@android.com>, Robert Love <rlove@google.com>, Mel Gorman <mel@csn.ul.ie>, Hugh Dickins <hughd@google.com>, Dave Hansen <dave@linux.vnet.ibm.com>, Rik van Riel <riel@redhat.com>, Dave Chinner <david@fromorbit.com>, Neil Brown <neilb@suse.de>, Mike Hommey <mh@glandium.org>, Taras Glek <tglek@mozilla.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, sanjay@google.com, David Rientjes <rientjes@google.com>

On Wed, Oct 31, 2012 at 06:56:05PM -0400, KOSAKI Motohiro wrote:
> glibc malloc discard freed memory by using MADV_DONTNEED
> as tcmalloc. and it is often a source of large performance decrease.
> because of MADV_DONTNEED discard memory immediately and
> right after malloc() call fall into page fault and pagesize memset() path.
> then, using DONTNEED increased zero fill and cache miss rate.

The memcg based solution that I posted a few months ago is working well
for us. We see significantly less cpu in zero'ing pages.

Not everyone was comfortable with the security implications of recycling
pages between processes in a memcg, although it was disabled by default
and had to be explicitly opted-in.

Also, memory allocators have a second motivation in using madvise: to
create virtually contiguous regions of memory from a fragmented address 
space, without increasing the RSS.

 -Arun

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