From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [PATCH 4/6] writeback: pay attention to wbc->nr_to_write in write_cache_pages Date: Tue, 8 Jun 2010 15:43:30 +1000 Message-ID: <20100608054330.GS26335@laptop> References: <1275957487-23633-1-git-send-email-david@fromorbit.com> <1275957487-23633-5-git-send-email-david@fromorbit.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, xfs@oss.sgi.com, akpm@linux-foundation.org To: Dave Chinner Return-path: Content-Disposition: inline In-Reply-To: <1275957487-23633-5-git-send-email-david@fromorbit.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, Jun 08, 2010 at 10:38:05AM +1000, Dave Chinner wrote: > From: Dave Chinner > > 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 > > This has adverse effects on filesystem writeback behaviour. write_cache_pages() > needs to terminate after a certain number of pages are written, not after a > certain number of calls to ->writepage are made. This is a regression > introduced by 17bc6c30cf6bfffd816bdc53682dd46fc34a2cf4 ("vfs: Add > no_nrwrite_index_update writeback control flag"), but cannot be reverted > directly due to subsequent bug fixes that have gone in on top of it. > > Signed-off-by: Dave Chinner > Reviewed-by: Christoph Hellwig Acked-by: Nick Piggin