The patch titled
readahead: backward prefetching method
has been added to the -mm tree. Its filename is
readahead-backward-prefetching-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: backward prefetching method
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Readahead policy for reading backward.
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
mm/readahead.c | 40 ++++++++++++++++++++++++++++++++++++++++
1 files changed, 40 insertions(+)
diff -puN mm/readahead.c~readahead-backward-prefetching-method mm/readahead.c
--- 25/mm/readahead.c~readahead-backward-prefetching-method Wed May 24 16:50:23 2006
+++ 25-akpm/mm/readahead.c Wed May 24 16:50:23 2006
@@ -1573,6 +1573,46 @@ initial_readahead(struct address_space *
}
/*
+ * Backward prefetching.
+ *
+ * No look-ahead and thrashing safety guard: should be unnecessary.
+ */
+static int
+try_read_backward(struct file_ra_state *ra, pgoff_t begin_index,
+ unsigned long ra_size, unsigned long ra_max)
+{
+ pgoff_t end_index;
+
+ /* Are we reading backward? */
+ if (begin_index > ra->prev_page)
+ return 0;
+
+ if ((ra->flags & RA_CLASS_MASK) == RA_CLASS_BACKWARD &&
+ ra_has_index(ra, ra->prev_page)) {
+ ra_size += 2 * ra_cache_hit(ra, 0);
+ end_index = ra->la_index;
+ } else {
+ ra_size += ra_size + ra_size * (readahead_hit_rate - 1) / 2;
+ end_index = ra->prev_page;
+ }
+
+ if (ra_size > ra_max)
+ ra_size = ra_max;
+
+ /* Read traces close enough to be covered by the prefetching? */
+ if (end_index > begin_index + ra_size)
+ return 0;
+
+ begin_index = end_index - ra_size;
+
+ ra_set_class(ra, RA_CLASS_BACKWARD);
+ ra_set_index(ra, begin_index, begin_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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