From: Wu Fengguang <fengguang.wu@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>,
Li Shaohua <shaohua.li@intel.com>,
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 8/9] readahead: basic support for backwards prefetching
Date: Tue, 29 Nov 2011 21:09:08 +0800 [thread overview]
Message-ID: <20111129131456.925952168@intel.com> (raw)
In-Reply-To: 20111129130900.628549879@intel.com
[-- Attachment #1: readahead-backwards.patch --]
[-- Type: text/plain, Size: 4300 bytes --]
Add the backwards prefetching feature. It's pretty simple if we don't
support async prefetching and interleaved reads.
Here is the behavior with an 8-page read sequence from 10000 down to 0.
(The readahead size is a bit large since it's an NFS mount.)
readahead-random(dev=0:16, ino=3948605, req=10000+8, ra=10000+8-0, async=0) = 8
readahead-backwards(dev=0:16, ino=3948605, req=9992+8, ra=9968+32-0, async=0) = 32
readahead-backwards(dev=0:16, ino=3948605, req=9960+8, ra=9840+128-0, async=0) = 128
readahead-backwards(dev=0:16, ino=3948605, req=9832+8, ra=9584+256-0, async=0) = 256
readahead-backwards(dev=0:16, ino=3948605, req=9576+8, ra=9072+512-0, async=0) = 512
readahead-backwards(dev=0:16, ino=3948605, req=9064+8, ra=8048+1024-0, async=0) = 1024
readahead-backwards(dev=0:16, ino=3948605, req=8040+8, ra=6128+1920-0, async=0) = 1920
readahead-backwards(dev=0:16, ino=3948605, req=6120+8, ra=4208+1920-0, async=0) = 1920
readahead-backwards(dev=0:16, ino=3948605, req=4200+8, ra=2288+1920-0, async=0) = 1920
readahead-backwards(dev=0:16, ino=3948605, req=2280+8, ra=368+1920-0, async=0) = 1920
readahead-backwards(dev=0:16, ino=3948605, req=360+8, ra=0+368-0, async=0) = 368
And a simple 1-page read sequence from 10000 down to 0.
readahead-random(dev=0:16, ino=3948605, req=10000+1, ra=10000+1-0, async=0) = 1
readahead-backwards(dev=0:16, ino=3948605, req=9999+1, ra=9996+4-0, async=0) = 4
readahead-backwards(dev=0:16, ino=3948605, req=9995+1, ra=9980+16-0, async=0) = 16
readahead-backwards(dev=0:16, ino=3948605, req=9979+1, ra=9916+64-0, async=0) = 64
readahead-backwards(dev=0:16, ino=3948605, req=9915+1, ra=9660+256-0, async=0) = 256
readahead-backwards(dev=0:16, ino=3948605, req=9659+1, ra=9148+512-0, async=0) = 512
readahead-backwards(dev=0:16, ino=3948605, req=9147+1, ra=8124+1024-0, async=0) = 1024
readahead-backwards(dev=0:16, ino=3948605, req=8123+1, ra=6204+1920-0, async=0) = 1920
readahead-backwards(dev=0:16, ino=3948605, req=6203+1, ra=4284+1920-0, async=0) = 1920
readahead-backwards(dev=0:16, ino=3948605, req=4283+1, ra=2364+1920-0, async=0) = 1920
readahead-backwards(dev=0:16, ino=3948605, req=2363+1, ra=444+1920-0, async=0) = 1920
readahead-backwards(dev=0:16, ino=3948605, req=443+1, ra=0+444-0, async=0) = 444
CC: Andi Kleen <andi@firstfloor.org>
CC: Li Shaohua <shaohua.li@intel.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
include/linux/fs.h | 2 ++
mm/readahead.c | 15 +++++++++++++++
2 files changed, 17 insertions(+)
--- linux-next.orig/include/linux/fs.h 2011-11-29 20:55:27.000000000 +0800
+++ linux-next/include/linux/fs.h 2011-11-29 20:57:07.000000000 +0800
@@ -968,6 +968,7 @@ struct file_ra_state {
* streams.
* RA_PATTERN_MMAP_AROUND read-around on mmap page faults
* (w/o any sequential/random hints)
+ * RA_PATTERN_BACKWARDS reverse reading detected
* RA_PATTERN_FADVISE triggered by POSIX_FADV_WILLNEED or FMODE_RANDOM
* RA_PATTERN_OVERSIZE a random read larger than max readahead size,
* do max readahead to break down the read size
@@ -978,6 +979,7 @@ enum readahead_pattern {
RA_PATTERN_SUBSEQUENT,
RA_PATTERN_CONTEXT,
RA_PATTERN_MMAP_AROUND,
+ RA_PATTERN_BACKWARDS,
RA_PATTERN_FADVISE,
RA_PATTERN_OVERSIZE,
RA_PATTERN_RANDOM,
--- linux-next.orig/mm/readahead.c 2011-11-29 20:57:03.000000000 +0800
+++ linux-next/mm/readahead.c 2011-11-29 20:57:07.000000000 +0800
@@ -23,6 +23,7 @@ static const char * const ra_pattern_nam
[RA_PATTERN_SUBSEQUENT] = "subsequent",
[RA_PATTERN_CONTEXT] = "context",
[RA_PATTERN_MMAP_AROUND] = "around",
+ [RA_PATTERN_BACKWARDS] = "backwards",
[RA_PATTERN_FADVISE] = "fadvise",
[RA_PATTERN_OVERSIZE] = "oversize",
[RA_PATTERN_RANDOM] = "random",
@@ -676,6 +677,20 @@ ondemand_readahead(struct address_space
}
/*
+ * backwards reading
+ */
+ if (offset < ra->start && offset + req_size >= ra->start) {
+ ra->pattern = RA_PATTERN_BACKWARDS;
+ ra->size = get_next_ra_size(ra, max);
+ max = ra->start;
+ if (ra->size > max)
+ ra->size = max;
+ ra->async_size = 0;
+ ra->start -= ra->size;
+ goto readit;
+ }
+
+ /*
* Query the page cache and look for the traces(cached history pages)
* that a sequential stream would leave behind.
*/
next prev parent reply other threads:[~2011-11-29 13:27 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-29 13:09 [PATCH 0/9] readahead stats/tracing, backwards prefetching and more (v2) Wu Fengguang
2011-11-29 13:09 ` [PATCH 1/9] block: limit default readahead size for small devices Wu Fengguang
2011-11-29 13:09 ` [PATCH 2/9] readahead: snap readahead request to EOF Wu Fengguang
2011-11-29 14:29 ` Jan Kara
2011-11-30 1:06 ` Wu Fengguang
2011-11-30 11:37 ` Jan Kara
2011-11-30 12:06 ` Wu Fengguang
2011-11-29 13:09 ` [PATCH 3/9] readahead: record readahead patterns Wu Fengguang
2011-11-29 14:40 ` Jan Kara
2011-11-29 17:57 ` Andi Kleen
2011-11-30 1:18 ` Wu Fengguang
2011-12-15 8:55 ` [PATCH] proc: show readahead state in fdinfo Wu Fengguang
2011-12-15 9:49 ` Ingo Molnar
2011-11-29 13:09 ` [PATCH 4/9] readahead: tag mmap page fault call sites Wu Fengguang
2011-11-29 14:41 ` Jan Kara
2011-11-29 13:09 ` [PATCH 5/9] readahead: tag metadata " Wu Fengguang
2011-11-29 14:45 ` Jan Kara
2011-11-29 13:09 ` [PATCH 6/9] readahead: add /debug/readahead/stats Wu Fengguang
2011-11-29 15:21 ` Jan Kara
2011-11-30 0:44 ` Wu Fengguang
2011-12-14 6:36 ` Wu Fengguang
2011-12-19 16:32 ` Jan Kara
2011-12-21 1:29 ` Wu Fengguang
2011-12-21 4:06 ` Dave Chinner
2011-12-23 3:33 ` Wu Fengguang
2011-12-23 11:16 ` Jan Kara
2011-11-29 13:09 ` [PATCH 7/9] readahead: add vfs/readahead tracing event Wu Fengguang
2011-11-29 15:22 ` Jan Kara
2011-11-30 0:42 ` Wu Fengguang
2011-11-30 11:44 ` Jan Kara
2011-11-30 12:06 ` Wu Fengguang
2011-12-06 15:30 ` Christoph Hellwig
2011-12-07 9:18 ` Wu Fengguang
2011-12-08 9:03 ` [PATCH] writeback: show writeback reason with __print_symbolic Wu Fengguang
2011-11-29 13:09 ` Wu Fengguang [this message]
2011-11-29 15:35 ` [PATCH 8/9] readahead: basic support for backwards prefetching Jan Kara
2011-11-29 16:37 ` Pádraig Brady
2011-11-30 0:24 ` Wu Fengguang
2011-11-30 0:37 ` Wu Fengguang
2011-11-30 11:21 ` Jan Kara
2011-11-29 13:09 ` [PATCH 9/9] readahead: dont do start-of-file readahead after lseek() Wu Fengguang
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