From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wu Fengguang Subject: Re: [PATCH 7/8] writeback: sync old inodes first in background writeback Date: Thu, 22 Jul 2010 16:52:10 +0800 Message-ID: <20100722085210.GA26714@localhost> References: <1279545090-19169-1-git-send-email-mel@csn.ul.ie> <1279545090-19169-8-git-send-email-mel@csn.ul.ie> <20100719142145.GD12510@infradead.org> <20100719144046.GR13117@csn.ul.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , Dave Chinner , Chris Mason , Nick Piggin , Rik van Riel , Johannes Weiner , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Andrew Morton , Andrea Arcangeli , Minchan Kim To: Mel Gorman Return-path: Content-Disposition: inline In-Reply-To: <20100719144046.GR13117@csn.ul.ie> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org > Some insight on how the other writeback changes that are being floated > around might affect the number of dirty pages reclaim encounters would also > be helpful. Here is an interesting related problem about the wait_on_page_writeback() call inside shrink_page_list(): http://lkml.org/lkml/2010/4/4/86 The problem is, wait_on_page_writeback() is called too early in the direct reclaim path, which blocks many random/unrelated processes when some slow (USB stick) writeback is on the way. A simple dd can easily create a big range of dirty pages in the LRU list. Therefore priority can easily go below (DEF_PRIORITY - 2) in a typical desktop, which triggers the lumpy reclaim mode and hence wait_on_page_writeback(). I proposed this patch at the time, which was confirmed to solve the problem: --- linux-next.orig/mm/vmscan.c 2010-06-24 14:32:03.000000000 +0800 +++ linux-next/mm/vmscan.c 2010-07-22 16:12:34.000000000 +0800 @@ -1650,7 +1650,7 @@ static void set_lumpy_reclaim_mode(int p */ if (sc->order > PAGE_ALLOC_COSTLY_ORDER) sc->lumpy_reclaim_mode = 1; - else if (sc->order && priority < DEF_PRIORITY - 2) + else if (sc->order && priority < DEF_PRIORITY / 2) sc->lumpy_reclaim_mode = 1; else sc->lumpy_reclaim_mode = 0; However KOSAKI and Minchan raised concerns about raising the bar. I guess this new patch is more problem oriented and acceptable: --- linux-next.orig/mm/vmscan.c 2010-07-22 16:36:58.000000000 +0800 +++ linux-next/mm/vmscan.c 2010-07-22 16:39:57.000000000 +0800 @@ -1217,7 +1217,8 @@ static unsigned long shrink_inactive_lis count_vm_events(PGDEACTIVATE, nr_active); nr_freed += shrink_page_list(&page_list, sc, - PAGEOUT_IO_SYNC); + priority < DEF_PRIORITY / 3 ? + PAGEOUT_IO_SYNC : PAGEOUT_IO_ASYNC); } nr_reclaimed += nr_freed; Thanks, Fengguang -- 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/ . Don't email: email@kvack.org