From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id C35DC6B008C for ; Tue, 22 Nov 2011 21:15:25 -0500 (EST) Subject: Re: [PATCH 7/7] mm: compaction: Introduce sync-light migration for use by compaction From: Shaohua Li In-Reply-To: References: <1321900608-27687-1-git-send-email-mgorman@suse.de> <1321900608-27687-8-git-send-email-mgorman@suse.de> <1321945011.22361.335.camel@sli10-conroe> Content-Type: text/plain; charset="UTF-8" Date: Wed, 23 Nov 2011 10:25:49 +0800 Message-ID: <1322015149.22361.338.camel@sli10-conroe> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Nai Xia Cc: Mel Gorman , Linux-MM , Andrea Arcangeli , Minchan Kim , Jan Kara , Andy Isaacson , Johannes Weiner , Rik van Riel , LKML On Wed, 2011-11-23 at 10:01 +0800, Nai Xia wrote: > On Tue, Nov 22, 2011 at 2:56 PM, Shaohua Li wrote: > > On Tue, 2011-11-22 at 02:36 +0800, Mel Gorman wrote: > >> This patch adds a lightweight sync migrate operation MIGRATE_SYNC_LIGHT > >> mode that avoids writing back pages to backing storage. Async > >> compaction maps to MIGRATE_ASYNC while sync compaction maps to > >> MIGRATE_SYNC_LIGHT. For other migrate_pages users such as memory > >> hotplug, MIGRATE_SYNC is used. > >> > >> This avoids sync compaction stalling for an excessive length of time, > >> particularly when copying files to a USB stick where there might be > >> a large number of dirty pages backed by a filesystem that does not > >> support ->writepages. > > Hi, > > from my understanding, with this, even writes > > to /proc/sys/vm/compact_memory doesn't wait for pageout, is this > > intended? > > on the other hand, MIGRATE_SYNC_LIGHT now waits for pagelock and buffer > > lock, so could wait on page read. page read and page out have the same > > latency, why takes them different? > > So for the problem you raised, I think my suggestion to Mel is to adopt the > following logic: > > if (!trylock_page(page) && !PageUptodate(page)) > we are quite likely to block on read, so we > depend on yet another MIGRATE_SYNC_MODE to decide > if we really want to lock_page() and wait for this IO. > > How do you think ? assume the PageUptodate() is at the check for 'goto out'. yes, looks reasonable to me. And we need similar check for buffer_head. Thanks, Shaohua -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org