From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f175.google.com (mail-ig0-f175.google.com [209.85.213.175]) by kanga.kvack.org (Postfix) with ESMTP id 9EB9B6B0038 for ; Thu, 19 Mar 2015 15:42:47 -0400 (EDT) Received: by igcau2 with SMTP id au2so104202536igc.0 for ; Thu, 19 Mar 2015 12:42:47 -0700 (PDT) Received: from mail-ig0-x22d.google.com (mail-ig0-x22d.google.com. [2607:f8b0:4001:c05::22d]) by mx.google.com with ESMTPS id d19si2700796icc.71.2015.03.19.12.42.46 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 19 Mar 2015 12:42:46 -0700 (PDT) Received: by ignm3 with SMTP id m3so17127258ign.0 for ; Thu, 19 Mar 2015 12:42:46 -0700 (PDT) Date: Thu, 19 Mar 2015 12:42:44 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH V6] Allow compaction of unevictable pages In-Reply-To: <1426773430-31052-1-git-send-email-emunson@akamai.com> Message-ID: References: <1426773430-31052-1-git-send-email-emunson@akamai.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Eric B Munson Cc: Andrew Morton , Vlastimil Babka , Thomas Gleixner , Christoph Lameter , Peter Zijlstra , Mel Gorman , 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 On Thu, 19 Mar 2015, 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 > faults after a page is present can set compact_unevictable to 0 and > 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 > fragmenting memory. When the value is set to 1, allocations succeed. > > Signed-off-by: Eric B Munson > Cc: Vlastimil Babka > Cc: Thomas Gleixner > Cc: Christoph Lameter > Cc: Peter Zijlstra > Cc: Mel Gorman > Cc: David Rientjes > Cc: Rik van Riel > Cc: Michal Hocko > Cc: linux-rt-users@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: linux-api@vger.kernel.org > Cc: linux-kernel@vger.kernel.org Acked-by: David Rientjes -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org