From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id BBFB26B00C5 for ; Thu, 4 Nov 2010 12:05:56 -0400 (EDT) Message-ID: Subject: Re: 2.6.36 io bring the system to its knees In-Reply-To: Your message of "Tue, 02 Nov 2010 09:12:39 EDT." <20101102131239.GA8680@think> Date: Thu, 4 Nov 2010 12:05:41 -0400 From: Sanjoy Mahajan MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org To: Chris Mason Cc: Ingo Molnar , Pekka Enberg , Aidar Kultayev , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Andrew Morton , Jens Axboe , Peter.Zijl@MIT.EDU List-ID: > So this sounds like the backup is just thrashing your cache. I think it's more than that. Starting an rxvt shouldn't take 8 seconds, even with a cold cache. Actually, it does take a while, so you do have a point. I just did echo 3 > /proc/sys/vm/drop_caches and then started rxvt. That takes about 3 seconds (which seems long, but I don't know wherein that slowness lies), of which maybe 0.25 seconds is loading and running 'date': $ time rxvt -e date real 0m2.782s user 0m0.148s sys 0m0.032s The 8-second delay during the rsync must have at least two causes: (1) the cache is wiped out, and (2) the rxvt binary cannot be paged in quickly because the disk is doing lots of other I/O. Can the system someknow that paging in the rxvt binary and shared libraries is interactive I/O, because it was started by an interactive process, and therefore should take priority over the rsync? > Does rsync have the option to do an fadvise DONTNEED? I couldn't find one. It would be good to have a solution that is independent of the backup app. (The 'locate' cron job does a similar thrashing of the interactive response.) -Sanjoy `Until lions have their historians, tales of the hunt shall always glorify the hunters.' --African Proverb -- 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 policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org