From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 8 Oct 2007 09:54:33 +1000 From: David Chinner Subject: Re: [PATCH] remove throttle_vm_writeout() Message-ID: <20071007235433.GW995458@sgi.com> References: <1191501626.22357.14.camel@twins> <1191504186.22357.20.camel@twins> <1191516427.5574.7.camel@lappy> <20071004104650.d158121f.akpm@linux-foundation.org> <20071005123028.GA10372@mail.ustc.edu.cn> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071005123028.GA10372@mail.ustc.edu.cn> Sender: owner-linux-mm@kvack.org Return-Path: To: Fengguang Wu Cc: Andrew Morton , Peter Zijlstra , Miklos Szeredi , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Fri, Oct 05, 2007 at 08:30:28PM +0800, Fengguang Wu wrote: > The improvement could be: > - kswapd is now explicitly preferred to do the writeout; Careful. kswapd is much less efficient at writeout than pdflush because it does not do low->high offset writeback per address space. It just flushes the pages in LRU order and that turns writeback into a non-sequential mess. I/O sizes decrease substantially and throughput falls through the floor. So if you want kswapd to take over all the writeback, it needs to do writeback in the same manner as the background flushes. i.e. by grabbing page->mapping and flushing that in sequential order rather than just the page on the end of the LRU.... I documented the effect of kswapd taking over writeback in this paper (section 5.3): http://oss.sgi.com/projects/xfs/papers/ols2006/ols-2006-paper.pdf Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group -- 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