From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id B22D16B00C5 for ; Tue, 22 Nov 2011 21:01:56 -0500 (EST) Received: by vcbfk26 with SMTP id fk26so1201208vcb.14 for ; Tue, 22 Nov 2011 18:01:55 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1321945011.22361.335.camel@sli10-conroe> 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> Date: Wed, 23 Nov 2011 10:01:53 +0800 Message-ID: Subject: Re: [PATCH 7/7] mm: compaction: Introduce sync-light migration for use by compaction From: Nai Xia Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Shaohua Li Cc: Mel Gorman , Linux-MM , Andrea Arcangeli , Minchan Kim , Jan Kara , Andy Isaacson , Johannes Weiner , Rik van Riel , LKML 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 ? Thanks, Nai > > 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