From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933098Ab2ILXt3 (ORCPT ); Wed, 12 Sep 2012 19:49:29 -0400 Received: from mga02.intel.com ([134.134.136.20]:59909 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932958Ab2ILXon (ORCPT ); Wed, 12 Sep 2012 19:44:43 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.80,413,1344236400"; d="scan'208";a="202569365" Subject: Re: [PATCH 0/3 v2] mm: Batch page reclamation under shink_page_list From: Tim Chen To: Andrew Morton Cc: Mel Gorman , Minchan Kim , Johannes Weiner , KAMEZAWA Hiroyuki , Andrea Arcangeli , David Rientjes , Michal Hocko , Xiao Guangrong , Paul Gortmaker , Matthew Wilcox , "Kirill A. Shutemov" , Andi Kleen , linux-mm@kvack.org, linux-kernel , Alex Shi , Fengguang Wu In-Reply-To: <20120912122758.ad15e10f.akpm@linux-foundation.org> References: <1347293960.9977.70.camel@schen9-DESK> <20120912122758.ad15e10f.akpm@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" Date: Wed, 12 Sep 2012 16:44:42 -0700 Message-ID: <1347493482.9977.94.camel@schen9-DESK> Mime-Version: 1.0 X-Mailer: Evolution 2.32.3 (2.32.3-1.fc14) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2012-09-12 at 12:27 -0700, Andrew Morton wrote: > > That sounds good, although more details on the performance changes > would be appreciated - after all, that's the entire point of the > patchset. > > And we shouldn't only test for improvements - we should also test for > degradation. What workloads might be harmed by this change? I'd suggest > > - a single process which opens N files and reads one page from each > one, then repeats. So there are no contiguous LRU pages which share > the same ->mapping. Get some page reclaim happening, measure the > impact. > > - The batching means that we now do multiple passes over pageframes > where we used to do things in a single pass. Walking all those new > page lists will be expensive if they are lengthy enough to cause L1 > cache evictions. I need to address both your concerns and Mel's concerns about the downside of prolonging the holding page locks for the pages to be unmmaped for patch 1 in the series. I'll try to do some testing to see what kind of benefit I get by only batching operations under the i_mmap_mutex (i.e. patch 2 and 3 only) and not do batch unmap. Those other changes don't have the downsides of prolonged page locking and we can incorporate them with less risks. > > What would be a test for this? A simple, single-threaded walk > through a file, I guess? Thanks for your test suggestions. I will do tests along your suggestions when I generate the next iterations of the patch. I've been playing with these patches for a while and they are based on 3.4 kernel. I'll move them to 3.6 kernel in my next iteration. > > Mel's review comments were useful, thanks. Very much appreciate comments from you, Mel and Minchan. I'll try to incorporate them in my changes. Tim