From: Wu Fengguang <wfg@mail.ustc.edu.cn>
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org, Wu Fengguang <wfg@mail.ustc.edu.cn>
Subject: [PATCH 2/6] readahead: backward prefetching method fix
Date: Sun, 25 Jun 2006 21:07:06 +0800 [thread overview]
Message-ID: <351240952.82409@ustc.edu.cn> (raw)
Message-ID: <20060625130921.987235199@localhost.localdomain> (raw)
In-Reply-To: 20060625130704.464870100@localhost.localdomain
[-- Attachment #1: readahead-backward-prefetching-fix.patch --]
[-- Type: text/plain, Size: 1870 bytes --]
- 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 <wfg@mail.ustc.edu.cn>
---
--- 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);
/*
--
next prev parent reply other threads:[~2006-06-25 13:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20060625130704.464870100@localhost.localdomain>
2006-06-25 13:07 ` [PATCH 0/6] Adaptive readahead updates 3 Wu Fengguang
[not found] ` <20060625130921.549904049@localhost.localdomain>
2006-06-25 13:07 ` [PATCH 1/6] readahead: context based method - slow start Wu Fengguang
[not found] ` <20060626023529.GB6120@mail.ustc.edu.cn>
2006-06-26 2:35 ` [updated PATCH " Wu Fengguang
[not found] ` <20060625130921.987235199@localhost.localdomain>
2006-06-25 13:07 ` Wu Fengguang [this message]
[not found] ` <20060625130922.216691316@localhost.localdomain>
2006-06-25 13:07 ` [PATCH 3/6] readahead: kconfig option READAHEAD_ALLOW_OVERHEADS Wu Fengguang
[not found] ` <20060625130922.816467605@localhost.localdomain>
2006-06-25 13:07 ` [PATCH 5/6] readahead: kconfig option READAHEAD_HIT_FEEDBACK Wu Fengguang
[not found] ` <20060625130923.154258797@localhost.localdomain>
2006-06-25 13:07 ` [PATCH 6/6] readahead: remove the size limit of max_sectors_kb on read_ahead_kb Wu Fengguang
[not found] ` <20060626015256.GA6120@mail.ustc.edu.cn>
2006-06-26 1:52 ` [PATCH 0/6] Adaptive readahead updates 3 Wu Fengguang
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