From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx197.postini.com [74.125.245.197]) by kanga.kvack.org (Postfix) with SMTP id 730C96B13F0 for ; Tue, 31 Jan 2012 09:47:44 -0500 (EST) Date: Tue, 31 Jan 2012 09:47:34 -0500 From: Vivek Goyal Subject: Re: [PATCH] fix readahead pipeline break caused by block plug Message-ID: <20120131144734.GA4378@redhat.com> References: <1327996780.21268.42.camel@sli10-conroe> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1327996780.21268.42.camel@sli10-conroe> Sender: owner-linux-mm@kvack.org List-ID: To: Shaohua Li Cc: lkml , linux-mm , Andrew Morton , Jens Axboe , Herbert Poetzl , Eric Dumazet , Wu Fengguang On Tue, Jan 31, 2012 at 03:59:40PM +0800, Shaohua Li wrote: > Herbert Poetzl reported a performance regression since 2.6.39. The test > is a simple dd read, but with big block size. The reason is: > > T1: ra (A, A+128k), (A+128k, A+256k) > T2: lock_page for page A, submit the 256k > T3: hit page A+128K, ra (A+256k, A+384). the range isn't submitted > because of plug and there isn't any lock_page till we hit page A+256k > because all pages from A to A+256k is in memory > T4: hit page A+256k, ra (A+384, A+ 512). Because of plug, the range isn't > submitted again. Why IO is not submitted because of plug? Doesn't task now get scheduled out causing an unplug? IOW, are we now busy waiting somewhere preventing unplug? Thanks Vivek -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org