From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753196Ab2ILUHy (ORCPT ); Wed, 12 Sep 2012 16:07:54 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:39426 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752132Ab2ILUHe (ORCPT ); Wed, 12 Sep 2012 16:07:34 -0400 Date: Wed, 12 Sep 2012 13:07:32 -0700 From: Andrew Morton To: Minchan Kim Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Kyungmin Park , Marek Szyprowski , Michal Nazarewicz , Rik van Riel , Mel Gorman Subject: Re: [PATCH] mm: cma: Discard clean pages during contiguous allocation instead of migration Message-Id: <20120912130732.99ecf764.akpm@linux-foundation.org> In-Reply-To: <1347324112-14134-1-git-send-email-minchan@kernel.org> References: <1347324112-14134-1-git-send-email-minchan@kernel.org> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; 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 Tue, 11 Sep 2012 09:41:52 +0900 Minchan Kim wrote: > This patch drops clean cache pages instead of migration during > alloc_contig_range() to minimise allocation latency by reducing the amount > of migration is necessary. It's useful for CMA because latency of migration > is more important than evicting the background processes working set. > In addition, as pages are reclaimed then fewer free pages for migration > targets are required so it avoids memory reclaiming to get free pages, > which is a contributory factor to increased latency. > > * from v1 > * drop migrate_mode_t > * add reclaim_clean_pages_from_list instad of MIGRATE_DISCARD support - Mel > > I measured elapsed time of __alloc_contig_migrate_range which migrates > 10M in 40M movable zone in QEMU machine. > > Before - 146ms, After - 7ms > > ... > > @@ -758,7 +760,9 @@ static unsigned long shrink_page_list(struct list_head *page_list, > wait_on_page_writeback(page); > } > > - references = page_check_references(page, sc); > + if (!force_reclaim) > + references = page_check_references(page, sc); grumble. Could we please document `enum page_references' and page_check_references()? And the `force_reclaim' arg could do with some documentation. It only forces reclaim under certain circumstances. They should be described, and a reson should be provided. Why didn't this patch use PAGEREF_RECLAIM_CLEAN? It is possible for someone to dirty one of these pages after we tested its cleanness and we'll then go off and write it out, but we won't be reclaiming it? > > ... >