From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 17/18] writeback: fix dirtied pages accounting on redirty Date: Wed, 07 Sep 2011 10:19:47 +0200 Message-ID: <1315383587.11101.18.camel@twins> References: <20110904015305.367445271@intel.com> <20110904020916.841463184@intel.com> <1315325936.14232.22.camel@twins> <20110907002222.GF31945@quack.suse.cz> <20110907065635.GA12619@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Cc: Jan Kara , Wu Fengguang , linux-fsdevel@vger.kernel.org, Andrew Morton , Dave Chinner , Greg Thelen , Minchan Kim , Vivek Goyal , Andrea Righi , linux-mm , LKML To: Christoph Hellwig Return-path: In-Reply-To: <20110907065635.GA12619@lst.de> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Wed, 2011-09-07 at 08:56 +0200, Christoph Hellwig wrote: > On Wed, Sep 07, 2011 at 02:22:22AM +0200, Jan Kara wrote: > > > So wtf is ext4 doing? Shouldn't a page stay dirty until its written o= ut? > > >=20 > > > That is, should we really frob around this behaviour or fix ext4 beca= use > > > its on crack? > > Fengguang, could you please verify your findings with recent kernel? = I > > believe ext4 got fixed in this regard some time ago already (and yes, o= ld > > delalloc writeback code in ext4 was terrible). >=20 > The pattern we do in writeback is: >=20 > in pageout / write_cache_pages: > lock_page(); > clear_page_dirty_for_io(); >=20 > in ->writepage: > set_page_writeback(); > unlock_page(); > end_page_writeback(); >=20 > So whenever ->writepage decides it doesn't want to write things back > we have to redirty pages. We have this happen quite a bit in every > filesystem, but ext4 hits it a lot more than usual because it refuses > to write out delalloc pages from plain ->writepage and only allows > ->writepages to do it. Ah, right, so it is a fairly common thing and not something easily fixed in filesystems. Ok so I guess the patch is good. Thanks! -- 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