From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 97A946B01F8 for ; Thu, 19 Aug 2010 10:37:13 -0400 (EDT) Date: Thu, 19 Aug 2010 10:37:10 -0400 From: Christoph Hellwig Subject: Re: why are WB_SYNC_NONE COMMITs being done with FLUSH_SYNC set ? Message-ID: <20100819143710.GA4752@infradead.org> References: <20100819101525.076831ad@barsoom.rdu.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100819101525.076831ad@barsoom.rdu.redhat.com> Sender: owner-linux-mm@kvack.org To: Jeff Layton , fengguang.wu@gmail.com Cc: linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org List-ID: On Thu, Aug 19, 2010 at 10:15:25AM -0400, Jeff Layton wrote: > I'm looking at backporting some upstream changes to earlier kernels, > and ran across something I don't quite understand... > > In nfs_commit_unstable_pages, we set the flags to FLUSH_SYNC. We then > zero out the flags if wbc->nonblocking or wbc->for_background is set. > > Shouldn't we also clear it out if wbc->sync_mode == WB_SYNC_NONE ? > WB_SYNC_NONE means "don't wait on anything", so shouldn't that include > not waiting on the COMMIT to complete? I've been trying to figure out what the nonblocking flag is supposed to mean for a while now. It basically disappeared in commit 0d99519efef15fd0cf84a849492c7b1deee1e4b7 "writeback: remove unused nonblocking and congestion checks" from Wu. What's left these days is a couple of places in local copies of write_cache_pages (afs, cifs), and a couple of checks in random writepages instances (afs, block_write_full_page, ceph, nfs, reiserfs, xfs) and the use in nfs_write_inode. It's only actually set for memory migration and pageout, that is VM writeback. To me it really doesn't make much sense, but maybe someone has a better idea what it is for. > + if (wbc->nonblocking || wbc->for_background || > + wbc->sync_mode == WB_SYNC_NONE) You could remove the nonblocking and for_background checks as these impliy WB_SYNC_NONE. -- 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