From: Wu Fengguang <fengguang.wu@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Wu Fengguang <fengguang.wu@intel.com>
Cc: Linux Memory Management List <linux-mm@kvack.org>,
<linux-fsdevel@vger.kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH 7/9] readahead: dont do start-of-file readahead after lseek()
Date: Sat, 11 Feb 2012 12:31:47 +0800 [thread overview]
Message-ID: <20120211043326.371113915@intel.com> (raw)
In-Reply-To: 20120211043140.108656864@intel.com
[-- Attachment #1: readahead-lseek.patch --]
[-- Type: text/plain, Size: 2250 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 | 4 ++++
3 files changed, 8 insertions(+)
--- linux-next.orig/mm/readahead.c 2012-02-11 12:30:59.000000000 +0800
+++ linux-next/mm/readahead.c 2012-02-11 12:31:05.000000000 +0800
@@ -485,6 +485,7 @@ unsigned long ra_submit(struct file_ra_s
ra->pattern, ra->start, ra->size, ra->async_size,
actual);
+ ra->lseek = 0;
ra->for_mmap = 0;
ra->for_metadata = 0;
return actual;
@@ -636,6 +637,8 @@ ondemand_readahead(struct address_space
* start of file
*/
if (!offset) {
+ if (ra->lseek && req_size < max)
+ goto random_read;
ra->pattern = RA_PATTERN_INITIAL;
goto initial_readahead;
}
@@ -701,6 +704,7 @@ ondemand_readahead(struct address_space
if (try_context_readahead(mapping, ra, offset, req_size, max))
goto readit;
+random_read:
/*
* standalone, small random read
*/
--- linux-next.orig/fs/read_write.c 2012-02-11 12:30:59.000000000 +0800
+++ linux-next/fs/read_write.c 2012-02-11 12:31:05.000000000 +0800
@@ -47,6 +47,9 @@ static loff_t lseek_execute(struct file
file->f_pos = offset;
file->f_version = 0;
}
+
+ file->f_ra.lseek = 1;
+
return offset;
}
--- linux-next.orig/include/linux/fs.h 2012-02-11 12:30:59.000000000 +0800
+++ linux-next/include/linux/fs.h 2012-02-11 12:31:05.000000000 +0800
@@ -956,6 +956,7 @@ struct file_ra_state {
u8 pattern; /* one of RA_PATTERN_* */
unsigned int for_mmap:1; /* readahead for mmap accesses */
unsigned int for_metadata:1; /* readahead for meta data */
+ unsigned int lseek:1; /* this read has a leading lseek */
loff_t prev_pos; /* Cache last read() position */
};
next prev parent reply other threads:[~2012-02-11 9:51 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-11 4:31 [PATCH 0/9] readahead stats/tracing, backwards prefetching and more (v5) Wu Fengguang
2012-02-11 4:31 ` [PATCH 1/9] readahead: make context readahead more conservative Wu Fengguang
2012-02-11 4:31 ` [PATCH 2/9] readahead: record readahead patterns Wu Fengguang
2012-02-11 4:31 ` [PATCH 3/9] readahead: tag mmap page fault call sites Wu Fengguang
2012-02-11 4:31 ` [PATCH 4/9] readahead: tag metadata " Wu Fengguang
2012-02-11 4:31 ` [PATCH 5/9] readahead: add vfs/readahead tracing event Wu Fengguang
2012-02-11 4:31 ` [PATCH 6/9] readahead: add /debug/readahead/stats Wu Fengguang
2012-02-11 4:31 ` Wu Fengguang [this message]
2012-02-11 4:31 ` [PATCH 8/9] readahead: snap readahead request to EOF Wu Fengguang
2012-02-11 4:31 ` [PATCH 9/9] readahead: basic support for backwards prefetching Wu Fengguang
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