The patch titled
readahead: sysctl parameters
has been added to the -mm tree. Its filename is
readahead-sysctl-parameters.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: readahead: sysctl parameters
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Add new sysctl entries in /proc/sys/vm:
- readahead_ratio = 50
i.e. set read-ahead size to <=(readahead_ratio%) thrashing threshold
- readahead_hit_rate = 1
i.e. read-ahead hit ratio >=(1/readahead_hit_rate) is deemed ok
readahead_ratio also provides a way to select read-ahead logic at runtime:
condition action
==========================================================================
readahead_ratio == 0 disable read-ahead
readahead_ratio <= 9 select the (old) stock read-ahead logic
readahead_ratio >= 10 select the (new) adaptive read-ahead logic
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
Documentation/sysctl/vm.txt | 37 ++++++++++++++++++++++++++++++++++
include/linux/sysctl.h | 2 +
kernel/sysctl.c | 28 +++++++++++++++++++++++++
mm/readahead.c | 17 +++++++++++++++
4 files changed, 84 insertions(+)
diff -puN Documentation/sysctl/vm.txt~readahead-sysctl-parameters Documentation/sysctl/vm.txt
--- 25/Documentation/sysctl/vm.txt~readahead-sysctl-parameters Wed May 24 16:49:25 2006
+++ 25-akpm/Documentation/sysctl/vm.txt Wed May 24 16:49:25 2006
@@ -31,6 +31,8 @@ Currently, these files are in /proc/sys/
- zone_reclaim_interval
- panic_on_oom
- swap_prefetch
+- readahead_ratio
+- readahead_hit_rate
==============================================================
@@ -202,3 +204,38 @@ copying back pages from swap into the sw
practice it can take many minutes before the vm is idle enough.
The default value is 1.
+
+==============================================================
+
+readahead_ratio
+
+This limits readahead size to percent of the thrashing threshold.
+The thrashing threshold is dynamicly estimated from the _history_ read
+speed and system load, to deduce the _future_ readahead request size.
+
+Set it to a smaller value if you have not enough memory for all the
+concurrent readers, or the I/O loads fluctuate a lot. But if there's
+plenty of memory(>2MB per reader), a bigger value may help performance.
+
+readahead_ratio also selects the readahead logic:
+ VALUE CODE PATH
+ -------------------------------------------
+ 0 disable readahead totally
+ 1-9 select the stock readahead logic
+ 10-inf select the adaptive readahead logic
+
+The default value is 50. Reasonable values would be [50, 100].
+
+==============================================================
+
+readahead_hit_rate
+
+This is the max allowed value of (readahead-pages : accessed-pages).
+Useful only when (readahead_ratio >= 10). If the previous readahead
+request has bad hit rate, the kernel will be reluctant to do the next
+readahead.
+
+Larger values help catch more sparse access patterns. Be aware that
+readahead of the sparse patterns sacrifices memory for speed.
+
+The default value is 1. It is recommended to keep the value below 16.
diff -puN include/linux/sysctl.h~readahead-sysctl-parameters include/linux/sysctl.h
--- 25/include/linux/sysctl.h~readahead-sysctl-parameters Wed May 24 16:49:25 2006
+++ 25-akpm/include/linux/sysctl.h Wed May 24 16:49:25 2006
@@ -194,6 +194,8 @@ enum
VM_PANIC_ON_OOM=33, /* panic at out-of-memory */
VM_VDSO_ENABLED=34, /* map VDSO into new processes? */
VM_SWAP_PREFETCH=35, /* swap prefetch */
+ VM_READAHEAD_RATIO=36, /* percent of read-ahead size to thrashing-threshold */
+ VM_READAHEAD_HIT_RATE=37, /* one accessed page legitimizes so many read-ahead pages */
};
/* CTL_NET names: */
diff -puN kernel/sysctl.c~readahead-sysctl-parameters kernel/sysctl.c
--- 25/kernel/sysctl.c~readahead-sysctl-parameters Wed May 24 16:49:25 2006
+++ 25-akpm/kernel/sysctl.c Wed May 24 16:49:25 2006
@@ -76,6 +76,12 @@ extern int sysctl_drop_caches;
extern int percpu_pagelist_fraction;
extern int compat_log;
+#if defined(CONFIG_ADAPTIVE_READAHEAD)
+extern int readahead_ratio;
+extern int readahead_hit_rate;
+static int one = 1;
+#endif
+
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
int unknown_nmi_panic;
int nmi_watchdog_enabled;
@@ -1044,6 +1050,28 @@ static ctl_table vm_table[] = {
.proc_handler = &proc_dointvec,
},
#endif
+#ifdef CONFIG_ADAPTIVE_READAHEAD
+ {
+ .ctl_name = VM_READAHEAD_RATIO,
+ .procname = "readahead_ratio",
+ .data = &readahead_ratio,
+ .maxlen = sizeof(readahead_ratio),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ .strategy = &sysctl_intvec,
+ .extra1 = &zero,
+ },
+ {
+ .ctl_name = VM_READAHEAD_HIT_RATE,
+ .procname = "readahead_hit_rate",
+ .data = &readahead_hit_rate,
+ .maxlen = sizeof(readahead_hit_rate),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ .strategy = &sysctl_intvec,
+ .extra1 = &one,
+ },
+#endif
{ .ctl_name = 0 }
};
diff -puN mm/readahead.c~readahead-sysctl-parameters mm/readahead.c
--- 25/mm/readahead.c~readahead-sysctl-parameters Wed May 24 16:49:25 2006
+++ 25-akpm/mm/readahead.c Wed May 24 16:49:25 2006
@@ -20,6 +20,23 @@
#include <linux/nfsd/const.h>
/*
+ * Adaptive read-ahead parameters.
+ */
+
+/* In laptop mode, poll delayed look-ahead on every ## pages read. */
+#define LAPTOP_POLL_INTERVAL 16
+
+/* Set look-ahead size to 1/# of the thrashing-threshold. */
+#define LOOKAHEAD_RATIO 8
+
+/* Set read-ahead size to ##% of the thrashing-threshold. */
+int readahead_ratio = 50;
+EXPORT_SYMBOL_GPL(readahead_ratio);
+
+/* Readahead as long as cache hit ratio keeps above 1/##. */
+int readahead_hit_rate = 1;
+
+/*
* Detailed classification of read-ahead behaviors.
*/
#define RA_CLASS_SHIFT 4
_
Patches currently in -mm which might be from wfg@xxxxxxxxxxxxxxxx are
readahead-kconfig-options.patch
radixtree-look-aside-cache.patch
radixtree-hole-scanning-functions.patch
readahead-page-flag-pg_readahead.patch
readahead-refactor-do_generic_mapping_read.patch
readahead-refactor-__do_page_cache_readahead.patch
readahead-insert-cond_resched-calls.patch
readahead-common-macros.patch
readahead-events-accounting.patch
readahead-support-functions.patch
readahead-sysctl-parameters.patch
readahead-min-max-sizes.patch
readahead-state-based-method-aging-accounting.patch
readahead-state-based-method-data-structure.patch
readahead-state-based-method-routines.patch
readahead-state-based-method.patch
readahead-context-based-method.patch
readahead-initial-method-guiding-sizes.patch
readahead-initial-method-thrashing-guard-size.patch
readahead-initial-method-expected-read-size.patch
readahead-initial-method-user-recommended-size.patch
readahead-initial-method.patch
readahead-backward-prefetching-method.patch
readahead-seeking-reads-method.patch
readahead-thrashing-recovery-method.patch
readahead-call-scheme.patch
readahead-laptop-mode.patch
readahead-loop-case.patch
readahead-nfsd-case.patch
readahead-turn-on-by-default.patch
readahead-debug-radix-tree-new-functions.patch
readahead-debug-traces-showing-accessed-file-names.patch
readahead-debug-traces-showing-read-patterns.patch
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