From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH V7] Allow compaction of unevictable pages Date: Fri, 20 Mar 2015 15:17:03 -0700 Message-ID: <20150320151703.dfd116931ddb397ade8bfd8c@linux-foundation.org> References: <1426859390-10974-1-git-send-email-emunson@akamai.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Vlastimil Babka , Thomas Gleixner , Christoph Lameter , Peter Zijlstra , Mel Gorman , David Rientjes , Rik van Riel , Michal Hocko , linux-doc@vger.kernel.org, linux-rt-users@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org To: Eric B Munson Return-path: In-Reply-To: <1426859390-10974-1-git-send-email-emunson@akamai.com> Sender: linux-doc-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org On Fri, 20 Mar 2015 09:49:50 -0400 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 this 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 > behavior with respect to the unevictable lru. Users that demand no page > faults after a page is present can set compact_unevictable_allowed to 0 > and users who need the large contiguous areas can enable compaction on > locked memory by leaving the default value of 1. Do we really really really need the /proc knob? We're already migrating these pages so users of mlock will occasionally see some latency - how likely is it that this patch will significantly damage anyone?