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Subject[PATCH 08/15] readahead: record readahead patterns
Record the readahead pattern in ra_flags. This info can be examined by
users via the readahead tracing/stats interfaces.

Currently 7 patterns are defined:

pattern readahead for
-----------------------------------------------------------
RA_PATTERN_INITIAL start-of-file/oversize read
RA_PATTERN_SUBSEQUENT trivial sequential read
RA_PATTERN_CONTEXT interleaved sequential read
RA_PATTERN_THRASH thrashed sequential read
RA_PATTERN_MMAP_AROUND mmap fault
RA_PATTERN_FADVISE posix_fadvise()
RA_PATTERN_RANDOM random read
CC: Ingo Molnar <mingo@elte.hu>
CC: Jens Axboe <jens.axboe@oracle.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
include/linux/fs.h | 32 ++++++++++++++++++++++++++++++++
include/linux/mm.h | 4 +++-
mm/filemap.c | 9 +++++++--
mm/readahead.c | 17 +++++++++++++----
4 files changed, 55 insertions(+), 7 deletions(-)
--- linux.orig/include/linux/fs.h 2010-02-24 10:44:44.000000000 +0800
+++ linux/include/linux/fs.h 2010-02-24 10:44:45.000000000 +0800
@@ -894,8 +894,40 @@ struct file_ra_state {
};

/* ra_flags bits */
+#define READAHEAD_PATTERN_SHIFT 20
+#define READAHEAD_PATTERN 0x00f00000
#define READAHEAD_MMAP_MISS 0x00000fff /* cache misses for mmap access */
#define READAHEAD_THRASHED 0x10000000
+#define READAHEAD_MMAP 0x20000000
+
+/*
+ * Which policy makes decision to do the current read-ahead IO?
+ */
+enum readahead_pattern {
+ RA_PATTERN_INITIAL,
+ RA_PATTERN_SUBSEQUENT,
+ RA_PATTERN_CONTEXT,
+ RA_PATTERN_THRASH,
+ RA_PATTERN_MMAP_AROUND,
+ RA_PATTERN_FADVISE,
+ RA_PATTERN_RANDOM,
+ RA_PATTERN_ALL, /* for summary stats */
+ RA_PATTERN_MAX
+};
+
+static inline int ra_pattern(int ra_flags)
+{
+ int pattern = (ra_flags & READAHEAD_PATTERN)
+ >> READAHEAD_PATTERN_SHIFT;
+
+ return min(pattern, RA_PATTERN_ALL);
+}
+
+static inline void ra_set_pattern(struct file_ra_state *ra, int pattern)
+{
+ ra->ra_flags = (ra->ra_flags & ~READAHEAD_PATTERN) |
+ (pattern << READAHEAD_PATTERN_SHIFT);
+}

/*
* Don't do ra_flags++ directly to avoid possible overflow:
--- linux.orig/mm/readahead.c 2010-02-24 10:44:44.000000000 +0800
+++ linux/mm/readahead.c 2010-02-24 10:44:45.000000000 +0800
@@ -339,7 +339,10 @@ unsigned long max_sane_readahead(unsigne
* Submit IO for the read-ahead request in file_ra_state.
*/
unsigned long ra_submit(struct file_ra_state *ra,
- struct address_space *mapping, struct file *filp)
+ struct address_space *mapping,
+ struct file *filp,
+ pgoff_t offset,
+ unsigned long req_size)
{
int actual;

@@ -473,6 +476,7 @@ ondemand_readahead(struct address_space
* start of file
*/
if (!offset) {
+ ra_set_pattern(ra, RA_PATTERN_INITIAL);
ra->start = offset;
ra->size = get_init_ra_size(req_size, max);
ra->async_size = ra->size > req_size ?
@@ -493,6 +497,7 @@ ondemand_readahead(struct address_space
*/
if ((offset == (ra->start + ra->size - ra->async_size) ||
offset == (ra->start + ra->size))) {
+ ra_set_pattern(ra, RA_PATTERN_SUBSEQUENT);
ra->start += ra->size;
ra->size = get_next_ra_size(ra, max);
ra->async_size = ra->size;
@@ -503,6 +508,7 @@ ondemand_readahead(struct address_space
* oversize read, no need to query page cache
*/
if (req_size > max && !hit_readahead_marker) {
+ ra_set_pattern(ra, RA_PATTERN_INITIAL);
ra->start = offset;
ra->size = max;
ra->async_size = max;
@@ -548,8 +554,10 @@ context_readahead:
*/
if (!size && !hit_readahead_marker) {
if (!ra_thrashed(ra, offset)) {
+ ra_set_pattern(ra, RA_PATTERN_RANDOM);
ra->size = min(req_size, max);
} else {
+ ra_set_pattern(ra, RA_PATTERN_THRASH);
retain_inactive_pages(mapping, offset, min(2 * max,
ra->start + ra->size - offset));
ra->size = max_t(int, ra->size/2, MIN_READAHEAD_PAGES);
@@ -566,12 +574,13 @@ context_readahead:
if (size >= offset)
size *= 2;
/*
- * pages to readahead are already cached
+ * Pages to readahead are already cached?
*/
if (size <= start - offset)
return 0;
-
size -= start - offset;
+
+ ra_set_pattern(ra, RA_PATTERN_CONTEXT);
ra->start = start;
ra->size = clamp_t(unsigned int, size, MIN_READAHEAD_PAGES, max);
ra->async_size = min(ra->size, 1 + size / READAHEAD_ASYNC_RATIO);
@@ -587,7 +596,7 @@ readit:
ra->size += ra->async_size;
}

- return ra_submit(ra, mapping, filp);
+ return ra_submit(ra, mapping, filp, offset, req_size);
}

/**
--- linux.orig/include/linux/mm.h 2010-02-24 10:44:41.000000000 +0800
+++ linux/include/linux/mm.h 2010-02-24 10:44:45.000000000 +0800
@@ -1208,7 +1208,9 @@ void page_cache_async_readahead(struct a
unsigned long max_sane_readahead(unsigned long nr);
unsigned long ra_submit(struct file_ra_state *ra,
struct address_space *mapping,
- struct file *filp);
+ struct file *filp,
+ pgoff_t offset,
+ unsigned long req_size);

/* Do stack extension */
extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
--- linux.orig/mm/filemap.c 2010-02-24 10:44:43.000000000 +0800
+++ linux/mm/filemap.c 2010-02-24 10:44:45.000000000 +0800
@@ -1413,6 +1413,7 @@ static void do_sync_mmap_readahead(struc

if (VM_SequentialReadHint(vma) ||
offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) {
+ ra->ra_flags |= READAHEAD_MMAP;
page_cache_sync_readahead(mapping, ra, file, offset,
ra->ra_pages);
return;
@@ -1431,10 +1432,12 @@ static void do_sync_mmap_readahead(struc
*/
ra_pages = max_sane_readahead(ra->ra_pages);
if (ra_pages) {
+ ra->ra_flags |= READAHEAD_MMAP;
+ ra_set_pattern(ra, RA_PATTERN_MMAP_AROUND);
ra->start = max_t(long, 0, offset - ra_pages/2);
ra->size = ra_pages;
ra->async_size = 0;
- ra_submit(ra, mapping, file);
+ ra_submit(ra, mapping, file, offset, 1);
}
}

@@ -1454,9 +1457,11 @@ static void do_async_mmap_readahead(stru
if (VM_RandomReadHint(vma))
return;
ra_mmap_miss_dec(ra);
- if (PageReadahead(page))
+ if (PageReadahead(page)) {
+ ra->ra_flags |= READAHEAD_MMAP;
page_cache_async_readahead(mapping, ra, file,
page, offset, ra->ra_pages);
+ }
}

/**



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