From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 12ACD6B0038 for ; Tue, 28 Nov 2017 18:34:21 -0500 (EST) Received: by mail-wm0-f69.google.com with SMTP id n126so570978wma.7 for ; Tue, 28 Nov 2017 15:34:21 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id l12si219385wrl.519.2017.11.28.15.34.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 Nov 2017 15:34:19 -0800 (PST) Date: Tue, 28 Nov 2017 15:34:16 -0800 From: Andrew Morton 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: Johannes Weiner , Mel Gorman , Joonsoo Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com 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? -- 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