The patch titled
readahead: backward prefetching method
has been removed from the -mm tree. Its filename was
readahead-backward-prefetching-method.patch
This patch was dropped because an updated version will be merged
------------------------------------------------------
Subject: readahead: backward prefetching method
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Readahead policy for reading backward.
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
DESC
readahead: backward prefetching method - add use case comment
EDESC
Backward prefetching is vital to structural analysis and some other
scientific applications. Comment this use case.
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
mm/readahead.c | 42 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)
diff -puN mm/readahead.c~readahead-backward-prefetching-method mm/readahead.c
--- a/mm/readahead.c~readahead-backward-prefetching-method
+++ a/mm/readahead.c
@@ -1579,6 +1579,48 @@ initial_readahead(struct address_space *
}
/*
+ * Backward prefetching.
+ *
+ * No look-ahead and thrashing safety guard: should be unnecessary.
+ *
+ * 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)
+{
+ 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->hit0;
+ 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-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
readahead-remove-size-limit-on-read_ahead_kb.patch
readahead-backward-prefetching-method-fix.patch
readahead-remove-the-size-limit-of-max_sectors_kb-on-read_ahead_kb.patch
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