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 ESMTP id 994BA6B01E3 for ; Fri, 16 Apr 2010 05:46:30 -0400 (EDT) Date: Fri, 16 Apr 2010 10:50:02 +0100 From: Alan Cox Subject: Re: [PATCH 1/4] vmscan: delegate pageout io to flusher thread if current is kswapd Message-ID: <20100416105002.191adeb1@lxorguk.ukuu.org.uk> In-Reply-To: <20100415233339.GW2493@dastard> References: <20100415013436.GO2493@dastard> <20100415130212.D16E.A69D9226@jp.fujitsu.com> <20100415131106.D174.A69D9226@jp.fujitsu.com> <64BE60A8-EEF9-4AC6-AF0A-0ED3CB544726@freebsd.org> <20100415093214.GV2493@dastard> <85DB7083-8E78-4884-9E76-5BD803C530EF@freebsd.org> <20100415233339.GW2493@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Dave Chinner Cc: Suleiman Souhlal , KOSAKI Motohiro , Mel Gorman , Chris Mason , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, suleiman@google.com List-ID: > No. If you are doing full disk seeks between random chunks, then you > still lose a large amount of throughput. e.g. if the seek time is > 10ms and your IO time is 10ms for each 4k page, then increasing the > size ito 64k makes it 10ms seek and 12ms for the IO. We might increase > throughput but we are still limited to 100 IOs per second. We've > gone from 400kB/s to 6MB/s, but that's still an order of magnitude > short of the 100MB/s full size IOs with little in way of seeks > between them will acheive on the same spindle... The usual armwaving numbers for ops/sec for an ATA disk are in the 200 ops/sec range so that seems horribly credible. But then I've never quite understood why our anonymous paging isn't sorting stuff as best it can and then using the drive as a log structure with in memory metadata so it can stream the pages onto disk. Read performance is goig to be similar (maybe better if you have a log tidy when idle), write ought to be far better. Alan -- 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