From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751249AbWFYNJP (ORCPT ); Sun, 25 Jun 2006 09:09:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751422AbWFYNJP (ORCPT ); Sun, 25 Jun 2006 09:09:15 -0400 Received: from smtp.ustc.edu.cn ([202.38.64.16]:3550 "HELO ustc.edu.cn") by vger.kernel.org with SMTP id S1751249AbWFYNJP (ORCPT ); Sun, 25 Jun 2006 09:09:15 -0400 Message-ID: <351240952.82409@ustc.edu.cn> X-EYOUMAIL-SMTPAUTH: wfg@mail.ustc.edu.cn Message-Id: <20060625130921.987235199@localhost.localdomain> References: <20060625130704.464870100@localhost.localdomain> Date: Sun, 25 Jun 2006 21:07:06 +0800 From: Wu Fengguang To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Wu Fengguang Subject: [PATCH 2/6] readahead: backward prefetching method fix Content-Disposition: inline; filename=readahead-backward-prefetching-fix.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org - The backward prefetching method fails near start of file. Fix it. - Make it scale up more quickly by adding ra_min to ra_size. - Do not discount readahead_hit_rate, that's not a documented behavior. Signed-off-by: Wu Fengguang --- --- linux-2.6.17-mm2.orig/mm/readahead.c +++ linux-2.6.17-mm2/mm/readahead.c @@ -1636,8 +1636,9 @@ initial_readahead(struct address_space * * Important for certain scientific arenas(i.e. structural analysis). */ static int -try_read_backward(struct file_ra_state *ra, pgoff_t begin_index, - unsigned long ra_size, unsigned long ra_max) +try_read_backward(struct file_ra_state *ra, + pgoff_t begin_index, unsigned long ra_size, + unsigned long ra_min, unsigned long ra_max) { pgoff_t end_index; @@ -1646,11 +1647,11 @@ try_read_backward(struct file_ra_state * return 0; if ((ra->flags & RA_CLASS_MASK) == RA_CLASS_BACKWARD && - ra_has_index(ra, ra->prev_page)) { - ra_size += 2 * ra->hit0; + ra_has_index(ra, ra->prev_page) && ra_cache_hit_ok(ra)) { + ra_size += ra_min + 2 * ra_readahead_size(ra); end_index = ra->la_index; } else { - ra_size += ra_size + ra_size * (readahead_hit_rate - 1) / 2; + ra_size += ra_size * readahead_hit_rate; end_index = ra->prev_page; } @@ -1661,7 +1662,7 @@ try_read_backward(struct file_ra_state * if (end_index > begin_index + ra_size) return 0; - begin_index = end_index - ra_size; + begin_index = end_index > ra_size ? end_index - ra_size : 0; ra_set_class(ra, RA_CLASS_BACKWARD); ra_set_index(ra, begin_index, begin_index); @@ -1864,7 +1865,7 @@ page_cache_readahead_adaptive(struct add * Backward read-ahead. */ if (!page && begin_index == index && - try_read_backward(ra, index, size, ra_max)) + try_read_backward(ra, index, size, ra_min, ra_max)) return ra_dispatch(ra, mapping, filp); /* --