The patch titled
readahead: initial method
has been added to the -mm tree. Its filename is
readahead-initial-method.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: initial method
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Aggressive readahead policy for read on start-of-file.
Instead of selecting a conservative readahead size,
it tries to do large readahead in the first place.
However we have to watch on two cases:
- do not ruin the hit rate for file-head-checkers
- do not lead to thrashing for memory tight systems
In most cases, the threat of file-head-peakers is neglectable. So a simple
user tunable parameter is used. Users can try a larger initial read-ahead
size:
echo 128 > /sys/block/sda/queue/initial_ra_kb
It benefits the many-small-files case:
adaptive readahead: avg 10.3 seconds
====================================
stock readahead: avg 12.3 seconds
=================================
The rxvt-unicode-7.7 being benchmarked is a dir with many .C/.h/.o files.
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
mm/readahead.c | 36 ++++++++++++++++++++++++++++++++++++
1 files changed, 36 insertions(+)
diff -puN mm/readahead.c~readahead-initial-method mm/readahead.c
--- a/mm/readahead.c~readahead-initial-method
+++ a/mm/readahead.c
@@ -1405,6 +1405,42 @@ has_history_pages:
}
/*
+ * Read-ahead on start of file.
+ *
+ * We want to be as aggressive as possible, _and_
+ * - do not ruin the hit rate for file-head-peekers
+ * - do not lead to thrashing for memory tight systems
+ */
+static unsigned long
+initial_readahead(struct address_space *mapping, struct file *filp,
+ struct file_ra_state *ra, unsigned long req_size)
+{
+ struct backing_dev_info *bdi = mapping->backing_dev_info;
+ unsigned long thrash_pages = bdi->ra_thrash_bytes >> PAGE_CACHE_SHIFT;
+ unsigned long ra_size;
+ unsigned long la_size;
+
+ ra_size = req_size;
+
+ /* user imposed minimal size */
+ if (ra_size < bdi->ra_pages0)
+ ra_size = bdi->ra_pages0;
+
+ /* no read-ahead thrashing */
+ if (ra_size > thrash_pages)
+ ra_size = thrash_pages;
+
+ /* do look-ahead on large(>= 32KB) read-ahead */
+ la_size = ra_size / LOOKAHEAD_RATIO;
+
+ ra_set_class(ra, RA_CLASS_INITIAL);
+ ra_set_index(ra, 0, 0);
+ ra_set_size(ra, ra_size, la_size);
+
+ return ra_submit(ra, mapping, filp);
+}
+
+/*
* ra_min is mainly determined by the size of cache memory. Reasonable?
*
* Table of concrete numbers for 4KB page size:
_
Patches currently in -mm which might be from wfg@xxxxxxxxxxxxxxxx are
readahead-kconfig-options.patch
radixtree-introduce-scan-hole-data-functions.patch
mm-introduce-probe_page.patch
mm-introduce-pg_readahead.patch
readahead-add-look-ahead-support-to-__do_page_cache_readahead.patch
readahead-insert-cond_resched-calls.patch
readahead-minmax_ra_pages.patch
readahead-events-accounting.patch
readahead-rescue_pages.patch
readahead-sysctl-parameters.patch
readahead-min-max-sizes.patch
readahead-state-based-method-aging-accounting.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-user-recommended-size.patch
readahead-initial-method.patch
readahead-backward-prefetching-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-remove-size-limit-on-read_ahead_kb.patch
readahead-remove-size-limit-of-max_sectors_kb-on-read_ahead_kb.patch
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