The patch titled
readahead: loop case
has been added to the -mm tree. Its filename is
readahead-loop-case.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: loop case
From: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Disable look-ahead for loop file.
Loopback files normally contain filesystems, in which case there are already
proper look-aheads in the upper layer, more look-aheads on the loopback file
only ruins the read-ahead hit rate.
Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
drivers/block/loop.c | 6 ++++++
include/linux/fs.h | 1 +
mm/readahead.c | 4 ++++
3 files changed, 11 insertions(+)
diff -puN drivers/block/loop.c~readahead-loop-case drivers/block/loop.c
--- a/drivers/block/loop.c~readahead-loop-case
+++ a/drivers/block/loop.c
@@ -755,6 +755,12 @@ static int loop_set_fd(struct loop_devic
mapping = file->f_mapping;
inode = mapping->host;
+ /* Instruct the readahead code to skip look-ahead on loop file.
+ * The upper layer should already do proper look-ahead,
+ * one more look-ahead here only ruins the cache hit rate.
+ */
+ file->f_ra.flags |= RA_FLAG_LOOP;
+
if (!(file->f_mode & FMODE_WRITE))
lo_flags |= LO_FLAGS_READ_ONLY;
diff -puN include/linux/fs.h~readahead-loop-case include/linux/fs.h
--- a/include/linux/fs.h~readahead-loop-case
+++ a/include/linux/fs.h
@@ -741,6 +741,7 @@ struct file_ra_state {
#define RA_FLAG_MISS (1UL<<31) /* a cache miss occured against this file */
#define RA_FLAG_INCACHE (1UL<<30) /* file is already in cache */
#define RA_FLAG_MMAP (1UL<<29) /* mmap page access */
+#define RA_FLAG_LOOP (1UL<<28) /* loopback file */
struct file {
/*
diff -puN mm/readahead.c~readahead-loop-case mm/readahead.c
--- a/mm/readahead.c~readahead-loop-case
+++ a/mm/readahead.c
@@ -950,6 +950,10 @@ static unsigned long ra_submit(struct fi
ra->lookahead_index = eof;
}
+ /* Disable look-ahead for loopback file. */
+ if (ra->flags & RA_FLAG_LOOP)
+ ra->lookahead_index = ra->readahead_index;
+
/* Take down the current read-ahead aging value. */
ra->age = nr_scanned_pages_node(numa_node_id());
_
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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