Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935449Ab0BZHiN (ORCPT ); Fri, 26 Feb 2010 02:38:13 -0500 Received: from mga11.intel.com ([192.55.52.93]:47188 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935431Ab0BZHiM (ORCPT ); Fri, 26 Feb 2010 02:38:12 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.49,545,1262592000"; d="scan'208";a="776120552" Date: Fri, 26 Feb 2010 15:38:04 +0800 From: Wu Fengguang To: Christian Ehrhardt Cc: Andrew Morton , Jens Axboe , Matt Mackall , Chris Mason , Peter Zijlstra , Clemens Ladisch , Olivier Galibert , Vivek Goyal , Nick Piggin , Linux Memory Management List , "linux-fsdevel@vger.kernel.org" , LKML , Rik van Riel Subject: Re: [PATCH 05/15] readahead: limit readahead size for small memory systems Message-ID: <20100226073804.GA7868@localhost> References: <20100224031001.026464755@intel.com> <20100224031054.307027163@intel.com> <4B869682.9010709@linux.vnet.ibm.com> <20100226022907.GA22226@localhost> <4B8776FC.30409@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B8776FC.30409@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2630 Lines: 65 Christian, On Fri, Feb 26, 2010 at 03:23:40PM +0800, Christian Ehrhardt wrote: > Unfortunately without a chance to measure this atm, this patch now looks > really good to me. > Thanks for adapting it to a read-ahead only per mem limit. > Acked-by: Christian Ehrhardt Thank you. Effective measurement is hard because it really depends on how the user want to stress use his small memory system ;) So I think a simple to understand and yet reasonable limit scheme would be OK. Thanks, Fengguang --- readahead: limit read-ahead size for small memory systems When lifting the default readahead size from 128KB to 512KB, make sure it won't add memory pressure to small memory systems. For read-ahead, the memory pressure is mainly readahead buffers consumed by too many concurrent streams. The context readahead can adapt readahead size to thrashing threshold well. So in principle we don't need to adapt the default _max_ read-ahead size to memory pressure. For read-around, the memory pressure is mainly read-around misses on executables/libraries. Which could be reduced by scaling down read-around size on fast "reclaim passes". This patch presents a straightforward solution: to limit default read-ahead size proportional to available system memory, ie. 512MB mem => 512KB read-around size 128MB mem => 128KB read-around size 32MB mem => 32KB read-around size This will allow power users to adjust read-ahead/read-around size at once, while saving the low end from unnecessary memory pressure, under the assumption that low end users have no need to request a large read-around size. CC: Matt Mackall Acked-by: Christian Ehrhardt Signed-off-by: Wu Fengguang --- mm/filemap.c | 2 +- mm/readahead.c | 22 ++++++++++++++++++++++ 2 files changed, 23 insertions(+), 1 deletion(-) --- linux.orig/mm/filemap.c 2010-02-26 10:04:28.000000000 +0800 +++ linux/mm/filemap.c 2010-02-26 10:08:33.000000000 +0800 @@ -1431,7 +1431,7 @@ static void do_sync_mmap_readahead(struc /* * mmap read-around */ - ra_pages = max_sane_readahead(ra->ra_pages); + ra_pages = min(ra->ra_pages, roundup_pow_of_two(totalram_pages / 1024)); if (ra_pages) { ra->start = max_t(long, 0, offset - ra_pages/2); ra->size = ra_pages; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/