From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlastimil Babka Subject: Re: [PATCH V6] Allow compaction of unevictable pages Date: Thu, 19 Mar 2015 15:56:14 +0100 Message-ID: <550AE38E.7090006@suse.cz> References: <1426773430-31052-1-git-send-email-emunson@akamai.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-2 Content-Transfer-Encoding: 7bit Cc: Thomas Gleixner , Christoph Lameter , Peter Zijlstra , Mel Gorman , David Rientjes , Rik van Riel , Michal Hocko , linux-rt-users-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Eric B Munson , Andrew Morton Return-path: In-Reply-To: <1426773430-31052-1-git-send-email-emunson-JqFfY2XvxFXQT0dZR+AlfA@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-rt-users.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.