From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id 9D5436B0069 for ; Tue, 22 Nov 2011 09:23:13 -0500 (EST) From: Jeff Moyer Subject: Re: [PATCH 1/8] block: limit default readahead size for small devices References: <20111121091819.394895091@intel.com> <20111121093846.121502745@intel.com> <20111121145247.0e37dc36.akpm@linux-foundation.org> Date: Tue, 22 Nov 2011 09:23:05 -0500 In-Reply-To: <20111121145247.0e37dc36.akpm@linux-foundation.org> (Andrew Morton's message of "Mon, 21 Nov 2011 14:52:47 -0800") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Wu Fengguang , Linux Memory Management List , linux-fsdevel@vger.kernel.org, Li Shaohua , Clemens Ladisch , Jens Axboe , Rik van Riel , LKML , Andi Kleen Andrew Morton writes: > In a better world, userspace would run a > work-out-what-readahead-size-to-use script each time a distro is > installed and when new storage devices are added/detected. Userspace > would then remember that readahead size for subsequent bootups. I'd be interested to hear what factors you think should be taken into account by such a script. I agree that there are certain things, like timing of reads of different sizes, or heuristics based on the size of installed memory, which could contribute to the default readahead size. However, other things, like memory pressure while running the desired workload, can't really be measured by an installer or one-time script. > In the real world, we shovel guaranteed-to-be-wrong guesswork into the > kernel and everyone just uses the results. Sigh. I'm not sure a userspace tool is the panacea you paint. However, if you can provide some guidance on what you think could make things better, I'm happy to give it a go. Cheers, Jeff -- 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