From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752016AbaEGVPk (ORCPT ); Wed, 7 May 2014 17:15:40 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:57367 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751010AbaEGVPg (ORCPT ); Wed, 7 May 2014 17:15:36 -0400 Date: Wed, 7 May 2014 14:15:34 -0700 From: Andrew Morton To: David Rientjes Cc: Mel Gorman , Rik van Riel , Vlastimil Babka , Joonsoo Kim , Greg Thelen , Hugh Dickins , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch v3 2/6] mm, compaction: return failed migration target pages back to freelist Message-Id: <20140507141534.d4def933b3a9999e7826df5c@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; 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, 6 May 2014 19:22:43 -0700 (PDT) David Rientjes wrote: > Memory compaction works by having a "freeing scanner" scan from one end of a > zone which isolates pages as migration targets while another "migrating scanner" > scans from the other end of the same zone which isolates pages for migration. > > When page migration fails for an isolated page, the target page is returned to > the system rather than the freelist built by the freeing scanner. This may > require the freeing scanner to continue scanning memory after suitable migration > targets have already been returned to the system needlessly. > > This patch returns destination pages to the freeing scanner freelist when page > migration fails. This prevents unnecessary work done by the freeing scanner but > also encourages memory to be as compacted as possible at the end of the zone. > > Reported-by: Greg Thelen What did Greg actually report? IOW, what if any observable problem is being fixed here?