From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 3EF9F6B01E5 for ; Tue, 15 Jun 2010 06:28:29 -0400 (EDT) Date: Tue, 15 Jun 2010 14:28:22 +0400 From: Evgeniy Polyakov Subject: Re: [PATCH 11/12] vmscan: Write out dirty pages in batch Message-ID: <20100615102822.GA4010@ioremap.net> References: <1276514273-27693-1-git-send-email-mel@csn.ul.ie> <1276514273-27693-12-git-send-email-mel@csn.ul.ie> <20100614231144.GG6590@dastard> <20100614162143.04783749.akpm@linux-foundation.org> <20100615003943.GK6590@dastard> <20100614183957.ad0cdb58.akpm@linux-foundation.org> <20100615032034.GR6590@dastard> <20100614211515.dd9880dc.akpm@linux-foundation.org> <20100615063643.GS6590@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100615063643.GS6590@dastard> Sender: owner-linux-mm@kvack.org To: Dave Chinner Cc: Andrew Morton , Mel Gorman , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Chris Mason , Nick Piggin , Rik van Riel , Johannes Weiner , Christoph Hellwig , KAMEZAWA Hiroyuki List-ID: On Tue, Jun 15, 2010 at 04:36:43PM +1000, Dave Chinner (david@fromorbit.com) wrote: > > Nope. Large-number-of-small-files is a pretty common case. If the fs > > doesn't handle that well (ie: by placing them nearby on disk), it's > > borked. > > Filesystems already handle this case just fine as we see it from > writeback all the time. Untarring a kernel is a good example of > this... > > I suggested sorting all the IO to be issued into per-mapping page > groups because: > a) makes IO issued from reclaim look almost exactly the same > to the filesytem as if writeback is pushing out the IO. > b) it looks to be a trivial addition to the new code. > > To me that's a no-brainer. That doesn't coverup large-number-of-small-files pattern, since untarring subsequently means creating something new, which FS can optimize. Much more interesting case is when we have dirtied large number of small files in kind-of random order and submitted them down to disk. Per-mapping sorting will not do anything good in this case, even if files were previously created in a good facion being placed closely and so on, and only block layer will find a correlation between adjacent blocks in different files. But with existing queue management it has quite a small opportunity, and that's what I think Andrew is arguing about. -- Evgeniy Polyakov -- 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