From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx157.postini.com [74.125.245.157]) by kanga.kvack.org (Postfix) with SMTP id ADD856B0081 for ; Mon, 21 May 2012 04:51:16 -0400 (EDT) Message-ID: <4FBA0203.20509@kernel.org> Date: Mon, 21 May 2012 17:51:15 +0900 From: Minchan Kim MIME-Version: 1.0 Subject: Re: [PATCH 1/2] swap: allow swap readahead to be merged References: <1337587755-4743-1-git-send-email-ehrhardt@linux.vnet.ibm.com> <1337587755-4743-2-git-send-email-ehrhardt@linux.vnet.ibm.com> In-Reply-To: <1337587755-4743-2-git-send-email-ehrhardt@linux.vnet.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: ehrhardt@linux.vnet.ibm.com Cc: linux-mm@kvack.org, axboe@kernel.dk On 05/21/2012 05:09 PM, ehrhardt@linux.vnet.ibm.com wrote: > From: Christian Ehrhardt > > Swap readahead works fine, but the I/O to disk is almost always done in page > size requests, despite the fact that readahead submits 1< at a time. > On older kernels the old per device plugging behavior might have captured > this and merged the requests, but currently all comes down to much more I/Os > than required. > > On a single device this might not be an issue, but as soon as a server runs > on shared san resources savin I/Os not only improves swapin throughput but > also provides a lower resource utilization. > > With a load running KVM in a lot of memory overcommitment (the hot memory > is 1.5 times the host memory) swapping throughput improves significantly > and the lead feels more responsive as well as achieves more throughput. > > In a test setup with 16 swap disks running blocktrace on one of those disks > shows the improved merging: > Prior: > Reads Queued: 560,888, 2,243MiB Writes Queued: 226,242, 904,968KiB > Read Dispatches: 544,701, 2,243MiB Write Dispatches: 159,318, 904,968KiB > Reads Requeued: 0 Writes Requeued: 0 > Reads Completed: 544,716, 2,243MiB Writes Completed: 159,321, 904,980KiB > Read Merges: 16,187, 64,748KiB Write Merges: 61,744, 246,976KiB > IO unplugs: 149,614 Timer unplugs: 2,940 > > With the patch: > Reads Queued: 734,315, 2,937MiB Writes Queued: 300,188, 1,200MiB > Read Dispatches: 214,972, 2,937MiB Write Dispatches: 215,176, 1,200MiB > Reads Requeued: 0 Writes Requeued: 0 > Reads Completed: 214,971, 2,937MiB Writes Completed: 215,177, 1,200MiB > Read Merges: 519,343, 2,077MiB Write Merges: 73,325, 293,300KiB > IO unplugs: 337,130 Timer unplugs: 11,184 > > Signed-off-by: Christian Ehrhardt > Acked-by: Rik van Riel > Acked-by: Jens Axboe Reviewed-by: Minchan Kim Didn't I add my Reviewed-by on your previous version? -- Kind regards, Minchan Kim -- 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