From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753249AbdK1XeU (ORCPT ); Tue, 28 Nov 2017 18:34:20 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:51946 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752471AbdK1XeS (ORCPT ); Tue, 28 Nov 2017 18:34:18 -0500 Date: Tue, 28 Nov 2017 15:34:16 -0800 From: Andrew Morton To: Vlastimil Babka Cc: Johannes Weiner , Mel Gorman , Joonsoo Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] mm, compaction: direct freepage allocation for async direct compaction Message-Id: <20171128153416.f7062caba47d86eb4eb15b8b@linux-foundation.org> In-Reply-To: <32b5f1b6-e3aa-4f15-4ec6-5cbb5fe158d0@suse.cz> References: <20171122143321.29501-1-hannes@cmpxchg.org> <32b5f1b6-e3aa-4f15-4ec6-5cbb5fe158d0@suse.cz> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 Nov 2017 15:52:55 +0100 Vlastimil Babka wrote: > On 11/22/2017 03:33 PM, Johannes Weiner wrote: > > From: Vlastimil Babka > > > > The goal of direct compaction is to quickly make a high-order page available > > for the pending allocation. The free page scanner can add significant latency > > when searching for migration targets, although to succeed the compaction, the > > only important limit on the target free pages is that they must not come from > > the same order-aligned block as the migrated pages. > > > > This patch therefore makes direct async compaction allocate freepages directly > > from freelists. Pages that do come from the same block (which we cannot simply > > exclude from the freelist allocation) are put on separate list and released > > only after migration to allow them to merge. > > > > In addition to reduced stall, another advantage is that we split larger free > > pages for migration targets only when smaller pages are depleted, while the > > free scanner can split pages up to (order - 1) as it encouters them. However, > > this approach likely sacrifices some of the long-term anti-fragmentation > > features of a thorough compaction, so we limit the direct allocation approach > > to direct async compaction. > > > > For observational purposes, the patch introduces two new counters to > > /proc/vmstat. compact_free_direct_alloc counts how many pages were allocated > > directly without scanning, and compact_free_direct_miss counts the subset of > > these allocations that were from the wrong range and had to be held on the > > separate list. > > > > Signed-off-by: Vlastimil Babka > > Signed-off-by: Johannes Weiner > > --- > > > > Hi. I'm resending this because we've been struggling with the cost of > > compaction in our fleet, and this patch helps substantially. > > > > On 128G+ machines, we have seen isolate_freepages_block() eat up 40% > > of the CPU cycles and scanning up to a billion PFNs per minute. Not in > > a spike, but continuously, to service higher-order allocations from > > the network stack, fork (non-vmap stacks), THP, etc. during regular > > operation. > > > > I've been running this patch on a handful of less-affected but still > > pretty bad machines for a week, and the results look pretty great: > > > > http://cmpxchg.org/compactdirectalloc/compactdirectalloc.png > > Thanks a lot, that's very encouraging! Yup. Should we proceed with this patch for now, or wait for something better to come along?