From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Aneesh Kumar K. V" Subject: Re: [PATCH 3/4] writeback: pay attention to wbc->nr_to_write in write_cache_pages Date: Fri, 30 Apr 2010 11:31:53 +0530 Message-ID: <87sk6dwka6.fsf@linux.vnet.ibm.com> References: <1271731314-5893-1-git-send-email-david@fromorbit.com> <1271731314-5893-4-git-send-email-david@fromorbit.com> <20100429143931.331c2bab.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, "Theodore Ts'o" , linux-kernel@vger.kernel.org, xfs@oss.sgi.com To: Andrew Morton , Dave Chinner Return-path: In-Reply-To: <20100429143931.331c2bab.akpm@linux-foundation.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com List-Id: linux-fsdevel.vger.kernel.org On Thu, 29 Apr 2010 14:39:31 -0700, Andrew Morton wrote: > On Tue, 20 Apr 2010 12:41:53 +1000 > Dave Chinner wrote: > > > If a filesystem writes more than one page in ->writepage, write_cache_pages > > fails to notice this and continues to attempt writeback when wbc->nr_to_write > > has gone negative - this trace was captured from XFS: > > > > > > wbc_writeback_start: towrt=1024 > > wbc_writepage: towrt=1024 > > wbc_writepage: towrt=0 > > wbc_writepage: towrt=-1 > > wbc_writepage: towrt=-5 > > wbc_writepage: towrt=-21 > > wbc_writepage: towrt=-85 > > > > Bug. > > AFAIT it's a regression introduced by > > : commit 17bc6c30cf6bfffd816bdc53682dd46fc34a2cf4 > : Author: Aneesh Kumar K.V > : AuthorDate: Thu Oct 16 10:09:17 2008 -0400 > : Commit: Theodore Ts'o > : CommitDate: Thu Oct 16 10:09:17 2008 -0400 > : > : vfs: Add no_nrwrite_index_update writeback control flag > > I suggest that what you do here is remove the local `nr_to_write' from > write_cache_pages() and go back to directly using wbc->nr_to_write > within the loop. > > And thus we restore the convention that if the fs writes back more than > a single page, it subtracts (nr_written - 1) from wbc->nr_to_write. > My mistake i never expected writepage to write more than one page. The interface said 'writepage' so it was natural to expect that it writes only one page. BTW the reason for the change is to give file system which accumulate dirty pages using write_cache_pages and attempt to write them out later a chance to properly manage nr_to_write. Something like ext4_da_writepages -- write_cache_pages ---- collect dirty page ---- return --return --now try to writeout all the collected dirty pages ( say 100) ----Only able to allocate blocks for 50 pages so update nr_to_write -= 50 and mark rest of 50 pages as dirty again So we want wbc->nr_to_write updated only by ext4_da_writepages. -aneesh _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs