From: Wu Fengguang <fengguang.wu@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <jens.axboe@oracle.com>,
Rik van Riel <riel@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Wu Fengguang <fengguang.wu@intel.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Clemens Ladisch <clemens@ladisch.de>
Cc: Olivier Galibert <galibert@pobox.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Linux Memory Management List <linux-mm@kvack.org>
Cc: <linux-fsdevel@vger.kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH 12/16] readahead: dont do start-of-file readahead after lseek()
Date: Mon, 01 Mar 2010 13:27:03 +0800 [thread overview]
Message-ID: <20100301053621.946764025@intel.com> (raw)
In-Reply-To: 20100301052651.857984880@intel.com
[-- Attachment #1: readahead-lseek.patch --]
[-- Type: text/plain, Size: 2307 bytes --]
Some applications (eg. blkid, id3tool etc.) seek around the file
to get information. For example, blkid does
seek to 0
read 1024
seek to 1536
read 16384
The start-of-file readahead heuristic is wrong for them, whose
access pattern can be identified by lseek() calls.
So test-and-set a READAHEAD_LSEEK flag on lseek() and don't
do start-of-file readahead on seeing it. Proposed by Linus.
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
fs/read_write.c | 3 +++
include/linux/fs.h | 1 +
mm/readahead.c | 5 +++++
3 files changed, 9 insertions(+)
--- linux.orig/mm/readahead.c 2010-03-01 13:23:45.000000000 +0800
+++ linux/mm/readahead.c 2010-03-01 13:23:45.000000000 +0800
@@ -670,6 +670,11 @@ ondemand_readahead(struct address_space
if (!offset) {
ra_set_pattern(ra, RA_PATTERN_INITIAL);
ra->start = offset;
+ if ((ra->ra_flags & READAHEAD_LSEEK) && req_size <= max) {
+ ra->size = req_size;
+ ra->async_size = 0;
+ goto readit;
+ }
ra->size = get_init_ra_size(req_size, max);
ra->async_size = ra->size > req_size ?
ra->size - req_size : ra->size;
--- linux.orig/fs/read_write.c 2010-03-01 13:21:43.000000000 +0800
+++ linux/fs/read_write.c 2010-03-01 13:23:45.000000000 +0800
@@ -71,6 +71,9 @@ generic_file_llseek_unlocked(struct file
file->f_version = 0;
}
+ if (!(file->f_ra.ra_flags & READAHEAD_LSEEK))
+ file->f_ra.ra_flags |= READAHEAD_LSEEK;
+
return offset;
}
EXPORT_SYMBOL(generic_file_llseek_unlocked);
--- linux.orig/include/linux/fs.h 2010-03-01 13:23:42.000000000 +0800
+++ linux/include/linux/fs.h 2010-03-01 13:23:45.000000000 +0800
@@ -899,6 +899,7 @@ struct file_ra_state {
#define READAHEAD_MMAP_MISS 0x00000fff /* cache misses for mmap access */
#define READAHEAD_THRASHED 0x10000000
#define READAHEAD_MMAP 0x20000000
+#define READAHEAD_LSEEK 0x40000000 /* be conservative after lseek() */
/*
* Which policy makes decision to do the current read-ahead IO?
--
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next prev parent reply other threads:[~2010-03-01 5:27 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-01 5:26 [PATCH 00/16] [PATCH 00/15] 512K readahead size with thrashing safe readahead v3 Wu Fengguang
2010-03-01 5:26 ` [PATCH 01/16] readahead: limit readahead size for small devices Wu Fengguang
2010-03-01 5:26 ` [PATCH 02/16] readahead: retain inactive lru pages to be accessed soon Wu Fengguang
2010-03-01 5:26 ` [PATCH 03/16] readahead: bump up the default readahead size Wu Fengguang
2010-03-01 5:26 ` [PATCH 04/16] readahead: make default readahead size a kernel parameter Wu Fengguang
2010-03-01 5:26 ` [PATCH 05/16] readahead: limit read-ahead size for small memory systems Wu Fengguang
2010-03-01 5:26 ` [PATCH 06/16] readahead: add notes on readahead size Wu Fengguang
2010-03-01 5:26 ` [PATCH 07/16] readahead: replace ra->mmap_miss with ra->ra_flags Wu Fengguang
2010-03-01 5:26 ` [PATCH 08/16] readahead: thrashing safe context readahead Wu Fengguang
2010-03-01 5:27 ` [PATCH 09/16] readahead: record readahead patterns Wu Fengguang
2010-03-01 5:27 ` [PATCH 10/16] readahead: add tracing event Wu Fengguang
2010-03-01 5:27 ` [PATCH 11/16] readahead: add /debug/readahead/stats Wu Fengguang
2010-03-01 5:27 ` Wu Fengguang [this message]
2010-03-01 5:27 ` [PATCH 13/16] radixtree: introduce radix_tree_lookup_leaf_node() Wu Fengguang
2010-03-01 5:27 ` [PATCH 14/16] radixtree: speed up the search for hole Wu Fengguang
2010-03-01 5:27 ` [PATCH 15/16] readahead: reduce MMAP_LOTSAMISS for mmap read-around Wu Fengguang
2010-03-01 5:27 ` [PATCH 16/16] readahead: pagecache context based " Wu Fengguang
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