From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754981Ab2A0Dlb (ORCPT ); Thu, 26 Jan 2012 22:41:31 -0500 Received: from mga14.intel.com ([143.182.124.37]:41153 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752178Ab2A0Dki (ORCPT ); Thu, 26 Jan 2012 22:40:38 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.71,315,1320652800"; d="scan'208";a="100232691" Message-Id: <20120127031327.567686120@intel.com> User-Agent: quilt/0.48-1 Date: Fri, 27 Jan 2012 11:05:33 +0800 From: Wu Fengguang To: Andrew Morton cc: Andi Kleen , Jan Kara , Wu Fengguang cc: Linux Memory Management List , Cc: LKML Subject: [PATCH 9/9] readahead: snap readahead request to EOF References: <20120127030524.854259561@intel.com> Content-Disposition: inline; filename=readahead-eof Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If the file size is 20kb and readahead request is [0, 16kb), it's better to expand the readahead request to [0, 20kb), which will likely save one followup I/O for the ending [16kb, 20kb). If the readahead request already covers EOF, trimm it down to EOF. Also don't set the PG_readahead mark to avoid an unnecessary future invocation of the readahead code. This special handling looks worthwhile because small to medium sized files are pretty common. Acked-by: Jan Kara Signed-off-by: Wu Fengguang --- mm/readahead.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) --- linux-next.orig/mm/readahead.c 2012-01-25 15:57:58.000000000 +0800 +++ linux-next/mm/readahead.c 2012-01-25 15:57:59.000000000 +0800 @@ -466,6 +466,25 @@ unsigned long max_sane_readahead(unsigne + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2); } +static void snap_to_eof(struct file_ra_state *ra, struct address_space *mapping) +{ + pgoff_t eof = ((i_size_read(mapping->host)-1) >> PAGE_CACHE_SHIFT) + 1; + pgoff_t start = ra->start; + unsigned int size = ra->size; + + /* + * skip backwards and random reads + */ + if (ra->pattern > RA_PATTERN_MMAP_AROUND) + return; + + size += min(size / 2, ra->ra_pages / 4); + if (start + size > eof) { + ra->size = eof - start; + ra->async_size = 0; + } +} + /* * Submit IO for the read-ahead request in file_ra_state. */ @@ -477,6 +496,8 @@ unsigned long ra_submit(struct file_ra_s { int actual; + snap_to_eof(ra, mapping); + actual = __do_page_cache_readahead(mapping, filp, ra->start, ra->size, ra->async_size);