From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755427AbbCSO4U (ORCPT ); Thu, 19 Mar 2015 10:56:20 -0400 Received: from cantor2.suse.de ([195.135.220.15]:49307 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750861AbbCSO4R (ORCPT ); Thu, 19 Mar 2015 10:56:17 -0400 Message-ID: <550AE38E.7090006@suse.cz> Date: Thu, 19 Mar 2015 15:56:14 +0100 From: Vlastimil Babka User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Eric B Munson , Andrew Morton CC: Thomas Gleixner , Christoph Lameter , Peter Zijlstra , Mel Gorman , David Rientjes , Rik van Riel , Michal Hocko , linux-rt-users@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V6] Allow compaction of unevictable pages References: <1426773430-31052-1-git-send-email-emunson@akamai.com> In-Reply-To: <1426773430-31052-1-git-send-email-emunson@akamai.com> Content-Type: text/plain; charset=iso-8859-2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/19/2015 02:57 PM, Eric B Munson wrote: > Currently, pages which are marked as unevictable are protected from > compaction, but not from other types of migration. The POSIX real time > extension explicitly states that mlock() will prevent a major page > fault, but the spirit of is is that mlock() should give a process the > ability to control sources of latency, including minor page faults. > However, the mlock manpage only explicitly says that a locked page will > not be written to swap and this can cause some confusion. The > compaction code today, does not give a developer who wants to avoid swap > but wants to have large contiguous areas available any method to achieve > this state. This patch introduces a sysctl for controlling compaction > behavoir with respect to the unevictable lru. Users that demand no page behavior > faults after a page is present can set compact_unevictable to 0 and compact_unevictable_allowed > users who need the large contiguous areas can enable compaction on > locked memory by leaving the default value of 1. > > To illustrate this problem I wrote a quick test program that mmaps a > large number of 1MB files filled with random data. These maps are > created locked and read only. Then every other mmap is unmapped and I > attempt to allocate huge pages to the static huge page pool. When the > compact_unevictable sysctl is 0, I cannot allocate hugepages after compact_unevictable_allowed > fragmenting memory. When the value is set to 1, allocations succeed. > > Signed-off-by: Eric B Munson > Cc: Vlastimil Babka Acked-by: Vlastimil Babka Thanks.