The patch titled
readahead: seeking reads method
has been added to the -mm tree. Its filename is
readahead-seeking-reads-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: seeking reads method
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Readahead policy on read after seeking.
It tries to detect sequences like:
seek(), 5*read(); seek(), 6*read(); seek(), 4*read(); ...
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
mm/readahead.c | 43 +++++++++++++++++++++++++++++++++++++++++++
1 files changed, 43 insertions(+)
diff -puN mm/readahead.c~readahead-seeking-reads-method mm/readahead.c
--- 25/mm/readahead.c~readahead-seeking-reads-method Wed May 24 16:50:27 2006
+++ 25-akpm/mm/readahead.c Wed May 24 16:50:27 2006
@@ -1613,6 +1613,49 @@ try_read_backward(struct file_ra_state *
}
/*
+ * If there is a previous sequential read, it is likely to be another
+ * sequential read at the new position.
+ *
+ * i.e. detect the following sequences:
+ * seek(), 5*read(); seek(), 6*read(); seek(), 4*read(); ...
+ *
+ * Databases are known to have this seek-and-read-N-pages pattern.
+ */
+static int
+try_readahead_on_seek(struct file_ra_state *ra, pgoff_t index,
+ unsigned long ra_size, unsigned long ra_max)
+{
+ unsigned long hit0 = ra_cache_hit(ra, 0);
+ unsigned long hit1 = ra_cache_hit(ra, 1) + hit0;
+ unsigned long hit2 = ra_cache_hit(ra, 2);
+ unsigned long hit3 = ra_cache_hit(ra, 3);
+
+ /* There's a previous read-ahead request? */
+ if (!ra_has_index(ra, ra->prev_page))
+ return 0;
+
+ /* The previous read-ahead sequences have similiar sizes? */
+ if (!(ra_size < hit1 && hit1 > hit2 / 2 &&
+ hit2 > hit3 / 2 &&
+ hit3 > hit1 / 2))
+ return 0;
+
+ hit1 = max(hit1, hit2);
+
+ /* Follow the same prefetching direction. */
+ if ((ra->flags & RA_CLASS_MASK) == RA_CLASS_BACKWARD)
+ index = ((index > hit1 - ra_size) ? index - hit1 + ra_size : 0);
+
+ ra_size = min(hit1, ra_max);
+
+ ra_set_class(ra, RA_CLASS_SEEK);
+ ra_set_index(ra, index, index);
+ ra_set_size(ra, ra_size, 0);
+
+ return 1;
+}
+
+/*
* 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-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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