From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:35040 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727735AbeKJAxj (ORCPT ); Fri, 9 Nov 2018 19:53:39 -0500 Date: Fri, 9 Nov 2018 07:12:39 -0800 From: Christoph Hellwig Subject: Re: [PATCH 01/16] xfs: drop ->writepage completely Message-ID: <20181109151239.GD9153@infradead.org> References: <20181107063127.3902-1-david@fromorbit.com> <20181107063127.3902-2-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181107063127.3902-2-david@fromorbit.com> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Dave Chinner Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org [adding linux-mm to the CC list] On Wed, Nov 07, 2018 at 05:31:12PM +1100, Dave Chinner wrote: > From: Dave Chinner > > ->writepage is only used in one place - single page writeback from > memory reclaim. We only allow such writeback from kswapd, not from > direct memory reclaim, and so it is rarely used. When it comes from > kswapd, it is effectively random dirty page shoot-down, which is > horrible for IO patterns. We will already have background writeback > trying to clean all the dirty pages in memory as efficiently as > possible, so having kswapd interrupt our well formed IO stream only > slows things down. So get rid of xfs_vm_writepage() completely. Interesting. IFF we can pull this off it would simplify a lot of things, so I'm generally in favor of it. ->writepage callers in generic code are: (1) mm/vmscan.c:pageout() - this is the kswaped (or direct reclaim) you mention above. It basically does nothing in this case which isn't great, but the whole point of this patch.. (2) mm/migrate.c:writeout() - this is only called if no ->migratepage method is presend, but we have one in XFS, so we should be ok. Plus a few pieces of code that are just library functions like generic_writepages and mpage_writepages.