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>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/readahead.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 46 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
@@ -1494,6 +1494,52 @@ initial_readahead(struct address_space *
return ra_submit(ra, mapping, filp);
}
+/*
+ * Backward prefetching.
+ *
+ * No look-ahead and thrashing safety guard: should be unnecessary.
+ *
+ * Important for certain scientific arenas(i.e. structural analysis).
+ */
+static int
+try_backward_prefetching(struct file_ra_state *ra, pgoff_t offset,
+ unsigned long size, unsigned long ra_max)
+{
+ pgoff_t prev = ra->prev_index;
+
+ /* Reading backward? */
+ if (offset >= prev)
+ return 0;
+
+ /* Close enough? */
+ size += readahead_hit_rate;
+ if (offset + 2 * size <= prev)
+ return 0;
+
+ if (ra_class_new(ra) == RA_CLASS_BACKWARD && ra_has_index(ra, prev)) {
+ prev = ra->la_index;
+ size += 2 * ra_readahead_size(ra);
+ } else
+ size *= 2;
+
+ if (size > ra_max)
+ size = ra_max;
+ if (size > prev)
+ size = prev;
+
+ /* The readahead-request covers the read-request? */
+ if (offset < prev - size)
+ return 0;
+
+ offset = prev - size;
+
+ ra_set_class(ra, RA_CLASS_BACKWARD);
+ ra_set_index(ra, offset, offset);
+ ra_set_size(ra, size, 0);
+
+ return 1;
+}
+
#endif /* CONFIG_ADAPTIVE_READAHEAD */
/*
_
Patches currently in -mm which might be from wfg@xxxxxxxxxxxxxxxx are
origin.patch
readahead-backward-prefetching-method.patch
readahead-thrashing-recovery-method.patch
readahead-thrashing-recovery-method-check-unbalanced-aging.patch
readahead-thrashing-recovery-method-refill-holes.patch
readahead-call-scheme.patch
readahead-call-scheme-cleanup.patch
readahead-call-scheme-catch-thrashing-on-lookahead-time.patch
readahead-call-scheme-doc-fixes-for-readahead.patch
readahead-laptop-mode.patch
readahead-loop-case.patch
readahead-nfsd-case.patch
readahead-remove-parameter-ra_max-from-thrashing_recovery_readahead.patch
readahead-remove-parameter-ra_max-from-adjust_rala.patch
readahead-state-based-method-protect-against-tiny-size.patch
readahead-rename-state_based_readahead-to-clock_based_readahead.patch
readahead-account-i-o-block-times-for-stock-readahead.patch
readahead-rescue_pages-updates.patch
readahead-remove-noaction-shrink-events.patch
readahead-remove-size-limit-on-read_ahead_kb.patch
readahead-remove-size-limit-of-max_sectors_kb-on-read_ahead_kb.patch
readahead-partial-sendfile-fix.patch
readahead-turn-on-by-default.patch
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