From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 3C4916B004A for ; Wed, 20 Jul 2011 01:53:19 -0400 (EDT) Received: by qwa26 with SMTP id 26so3397343qwa.14 for ; Tue, 19 Jul 2011 22:53:17 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1311130413.15392.326.camel@sli10-conroe> References: <1311130413.15392.326.camel@sli10-conroe> Date: Wed, 20 Jul 2011 14:53:16 +0900 Message-ID: Subject: Re: [PATCH]vmscan: add block plug for page reclaim From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Shaohua Li Cc: Jens Axboe , Andrew Morton , mgorman@suse.de, linux-mm , lkml On Wed, Jul 20, 2011 at 11:53 AM, Shaohua Li wrote: > per-task block plug can reduce block queue lock contention and increase request > merge. Currently page reclaim doesn't support it. I originally thought page > reclaim doesn't need it, because kswapd thread count is limited and file cache > write is done at flusher mostly. > When I test a workload with heavy swap in a 4-node machine, each CPU is doing > direct page reclaim and swap. This causes block queue lock contention. In my > test, without below patch, the CPU utilization is about 2% ~ 7%. With the > patch, the CPU utilization is about 1% ~ 3%. Disk throughput isn't changed. Why doesn't it enhance through? It means merge is rare? > This should improve normal kswapd write and file cache write too (increase > request merge for example), but might not be so obvious as I explain above. CPU utilization enhance on 4-node machine with heavy swap? I think it isn't common situation. And I don't want to add new stack usage if it doesn't have a benefit. As you know, direct reclaim path has a stack overflow. These days, Mel, Dave and Christoph try to remove write path in reclaim for solving stack usage and enhance write performance. -- 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