From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932188AbcLLJV2 (ORCPT ); Mon, 12 Dec 2016 04:21:28 -0500 Received: from mx2.suse.de ([195.135.220.15]:47188 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750712AbcLLJV1 (ORCPT ); Mon, 12 Dec 2016 04:21:27 -0500 Subject: Re: [PATCH] mm: fadvise: avoid expensive remote LRU cache draining after FADV_DONTNEED To: Johannes Weiner , Andrew Morton References: <20161210172658.5182-1-hannes@cmpxchg.org> Cc: Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com From: Vlastimil Babka Message-ID: <5cc0eb6f-bede-a34a-522b-e30d06723ffa@suse.cz> Date: Mon, 12 Dec 2016 10:21:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <20161210172658.5182-1-hannes@cmpxchg.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/10/2016 06:26 PM, Johannes Weiner wrote: > When FADV_DONTNEED cannot drop all pages in the range, it observes > that some pages might still be on per-cpu LRU caches after recent > instantiation and so initiates remote calls to all CPUs to flush their > local caches. However, in most cases, the fadvise happens from the > same context that instantiated the pages, and any pre-LRU pages in the > specified range are most likely sitting on the local CPU's LRU cache, > and so in many cases this results in unnecessary remote calls, which, > in a loaded system, can hold up the fadvise() call significantly. Got any numbers for this part? > Try to avoid the remote call by flushing the local LRU cache before > even attempting to invalidate anything. It's a cheap operation, and > the local LRU cache is the most likely to hold any pre-LRU pages in > the specified fadvise range. Anyway it looks like things can't be worse after this patch, so... > Signed-off-by: Johannes Weiner Acked-by: Vlastimil Babka > --- > mm/fadvise.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/mm/fadvise.c b/mm/fadvise.c > index 6c707bfe02fd..a43013112581 100644 > --- a/mm/fadvise.c > +++ b/mm/fadvise.c > @@ -139,7 +139,20 @@ SYSCALL_DEFINE4(fadvise64_64, int, fd, loff_t, offset, loff_t, len, int, advice) > } > > if (end_index >= start_index) { > - unsigned long count = invalidate_mapping_pages(mapping, > + unsigned long count; > + > + /* > + * It's common to FADV_DONTNEED right after > + * the read or write that instantiates the > + * pages, in which case there will be some > + * sitting on the local LRU cache. Try to > + * avoid the expensive remote drain and the > + * second cache tree walk below by flushing > + * them out right away. > + */ > + lru_add_drain(); > + > + count = invalidate_mapping_pages(mapping, > start_index, end_index); > > /* >