Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932226AbVLPMsW (ORCPT ); Fri, 16 Dec 2005 07:48:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932252AbVLPMrW (ORCPT ); Fri, 16 Dec 2005 07:47:22 -0500 Received: from ns.ustc.edu.cn ([202.38.64.1]:64142 "EHLO mx1.ustc.edu.cn") by vger.kernel.org with ESMTP id S932248AbVLPMrK (ORCPT ); Fri, 16 Dec 2005 07:47:10 -0500 Message-Id: <20051216131032.653462000@localhost.localdomain> References: <20051216130738.300284000@localhost.localdomain> Date: Fri, 16 Dec 2005 21:07:48 +0800 From: Wu Fengguang To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Wu Fengguang Subject: [PATCH 10/12] readahead: disable look-ahead for loopback file Content-Disposition: inline; filename=readahead-disable-lookahead-for-loopback.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2229 Lines: 69 Loopback files normally contain filesystem, in which case there are already proper look-aheads in the upper layer, more look-aheads on the loopback file only ruins the read-ahead hit rate. Signed-off-by: Wu Fengguang --- I'd like to thank Tero Grundstr?m for uncovering the loopback problem. drivers/block/loop.c | 6 ++++++ include/linux/fs.h | 1 + mm/readahead.c | 7 +++++++ 3 files changed, 14 insertions(+) --- linux.orig/include/linux/fs.h +++ linux/include/linux/fs.h @@ -631,6 +631,7 @@ struct file_ra_state { #define RA_FLAG_MISS 0x01 /* a cache miss occured against this file */ #define RA_FLAG_INCACHE 0x02 /* file is already in cache */ #define RA_FLAG_MMAP (1UL<<31) /* mmaped page access */ +#define RA_FLAG_NO_LOOKAHEAD (1UL<<30) /* disable look-ahead */ struct file { /* --- linux.orig/drivers/block/loop.c +++ linux/drivers/block/loop.c @@ -782,6 +782,12 @@ static int loop_set_fd(struct loop_devic mapping = file->f_mapping; inode = mapping->host; + /* + * The upper layer should already do proper look-ahead, + * one more look-ahead here only ruins the cache hit rate. + */ + file->f_ra.flags |= RA_FLAG_NO_LOOKAHEAD; + if (!(file->f_mode & FMODE_WRITE)) lo_flags |= LO_FLAGS_READ_ONLY; --- linux.orig/mm/readahead.c +++ linux/mm/readahead.c @@ -1191,6 +1191,10 @@ static inline void ra_set_index(struct f static inline void ra_set_size(struct file_ra_state *ra, unsigned long ra_size, unsigned long la_size) { + /* Disable look-ahead for loopback file. */ + if (unlikely(ra->flags & RA_FLAG_NO_LOOKAHEAD)) + la_size = 0; + ra->readahead_index = ra->ra_index + ra_size; ra->lookahead_index = ra->readahead_index - la_size; } @@ -1571,6 +1575,9 @@ static int query_page_cache(struct addre if (count < ra_max) goto out; + if (unlikely(ra->flags & RA_FLAG_NO_LOOKAHEAD)) + goto out; + /* * Check the far pages coarsely. * The big count here helps increase la_size. -- - 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/