Hi
This patch adds prefetch function to dm-bufio. I'm adding Joe to CC,
because he may use it in his code too.
Mikulas
---
dm-bufio: prefetch
This patch introduces a new function dm_bufio_prefetch. It prefetches
the specified range of blocks into dm-bufio cache without waiting
for i/o completion.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/md/dm-bufio.c | 88 +++++++++++++++++++++++++++++++++++++++-----------
drivers/md/dm-bufio.h | 8 ++++
2 files changed, 77 insertions(+), 19 deletions(-)
Index: linux-3.3-rc6-fast/drivers/md/dm-bufio.c
===================================================================
--- linux-3.3-rc6-fast.orig/drivers/md/dm-bufio.c 2012-03-12 22:20:47.000000000 +0100
+++ linux-3.3-rc6-fast/drivers/md/dm-bufio.c 2012-03-12 22:38:01.000000000 +0100
@@ -579,7 +579,7 @@ static void write_endio(struct bio *bio,
struct dm_buffer *b = container_of(bio, struct dm_buffer, bio);
b->write_error = error;
- if (error) {
+ if (unlikely(error)) {
struct dm_bufio_client *c = b->c;
(void)cmpxchg(&c->async_write_error, 0, error);
}
@@ -698,13 +698,20 @@ static void __wait_for_free_buffer(struc
dm_bufio_lock(c);
}
+enum new_flag {
+ NF_FRESH = 0,
+ NF_READ = 1,
+ NF_GET = 2,
+ NF_PREFETCH = 3
+};
+
/*
* Allocate a new buffer. If the allocation is not possible, wait until
* some other thread frees a buffer.
*
* May drop the lock and regain it.
*/
-static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c)
+static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c, enum new_flag nf)
{
struct dm_buffer *b;
@@ -727,6 +734,9 @@ static struct dm_buffer *__alloc_buffer_
return b;
}
+ if (nf == NF_PREFETCH)
+ return NULL;
+
if (!list_empty(&c->reserved_buffers)) {
b = list_entry(c->reserved_buffers.next,
struct dm_buffer, lru_list);
@@ -744,9 +754,12 @@ static struct dm_buffer *__alloc_buffer_
}
}
-static struct dm_buffer *__alloc_buffer_wait(struct dm_bufio_client *c)
+static struct dm_buffer *__alloc_buffer_wait(struct dm_bufio_client *c, enum new_flag nf)
{
- struct dm_buffer *b = __alloc_buffer_wait_no_callback(c);
+ struct dm_buffer *b = __alloc_buffer_wait_no_callback(c, nf);
+
+ if (!b)
+ return NULL;
if (c->alloc_callback)
c->alloc_callback(b);
@@ -866,15 +879,8 @@ static struct dm_buffer *__find(struct d
* Getting a buffer
*--------------------------------------------------------------*/
-enum new_flag {
- NF_FRESH = 0,
- NF_READ = 1,
- NF_GET = 2
-};
-
static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
- enum new_flag nf, struct dm_buffer **bp,
- int *need_submit)
+ enum new_flag nf, int *need_submit)
{
struct dm_buffer *b, *new_b = NULL;
@@ -882,6 +888,19 @@ static struct dm_buffer *__bufio_new(str
b = __find(c, block);
if (b) {
+found_buffer:
+ if (nf == NF_PREFETCH)
+ return NULL;
+ /*
+ * Note: it is essential that we don't wait for the buffer to be
+ * read if dm_bufio_get function is used. Both dm_bufio_get and
+ * dm_bufio_prefetch can be used in the driver request routine.
+ * If the user called both dm_bufio_prefetch and dm_bufio_get on
+ * the same buffer, it would deadlock if we waited.
+ */
+ if (nf == NF_GET && unlikely(test_bit(B_READING, &b->state)))
+ return NULL;
+
b->hold_count++;
__relink_lru(b, test_bit(B_DIRTY, &b->state) ||
test_bit(B_WRITING, &b->state));
@@ -891,7 +910,9 @@ static struct dm_buffer *__bufio_new(str
if (nf == NF_GET)
return NULL;
- new_b = __alloc_buffer_wait(c);
+ new_b = __alloc_buffer_wait(c, nf);
+ if (!new_b)
+ return NULL;
/*
* We've had a period where the mutex was unlocked, so need to
@@ -900,10 +921,7 @@ static struct dm_buffer *__bufio_new(str
b = __find(c, block);
if (b) {
__free_buffer_wake(new_b);
- b->hold_count++;
- __relink_lru(b, test_bit(B_DIRTY, &b->state) ||
- test_bit(B_WRITING, &b->state));
- return b;
+ goto found_buffer;
}
__check_watermark(c);
@@ -957,7 +975,7 @@ static void *new_read(struct dm_bufio_cl
struct dm_buffer *b;
dm_bufio_lock(c);
- b = __bufio_new(c, block, nf, bp, &need_submit);
+ b = __bufio_new(c, block, nf, &need_submit);
dm_bufio_unlock(c);
if (!b || IS_ERR(b))
@@ -1006,13 +1024,42 @@ void *dm_bufio_new(struct dm_bufio_clien
}
EXPORT_SYMBOL_GPL(dm_bufio_new);
+void dm_bufio_prefetch(struct dm_bufio_client *c,
+ sector_t block, unsigned n_blocks)
+{
+ struct blk_plug plug;
+
+ blk_start_plug(&plug);
+ dm_bufio_lock(c);
+
+ for (; n_blocks--; block++) {
+ int need_submit;
+ struct dm_buffer *b;
+ b = __bufio_new(c, block, NF_PREFETCH, &need_submit);
+ if (unlikely(b != NULL)) {
+ dm_bufio_unlock(c);
+
+ if (need_submit)
+ submit_io(b, READ, b->block, read_endio);
+ dm_bufio_release(b);
+
+ dm_bufio_cond_resched();
+ dm_bufio_lock(c);
+ }
+
+ }
+
+ dm_bufio_unlock(c);
+ blk_finish_plug(&plug);
+}
+EXPORT_SYMBOL(dm_bufio_prefetch);
+
void dm_bufio_release(struct dm_buffer *b)
{
struct dm_bufio_client *c = b->c;
dm_bufio_lock(c);
- BUG_ON(test_bit(B_READING, &b->state));
BUG_ON(!b->hold_count);
b->hold_count--;
@@ -1025,6 +1072,7 @@ void dm_bufio_release(struct dm_buffer *
* invalid buffer.
*/
if ((b->read_error || b->write_error) &&
+ !test_bit(B_READING, &b->state) &&
!test_bit(B_WRITING, &b->state) &&
!test_bit(B_DIRTY, &b->state)) {
__unlink_buffer(b);
@@ -1042,6 +1090,8 @@ void dm_bufio_mark_buffer_dirty(struct d
dm_bufio_lock(c);
+ BUG_ON(test_bit(B_READING, &b->state));
+
if (!test_and_set_bit(B_DIRTY, &b->state))
__relink_lru(b, LIST_DIRTY);
Index: linux-3.3-rc6-fast/drivers/md/dm-bufio.h
===================================================================
--- linux-3.3-rc6-fast.orig/drivers/md/dm-bufio.h 2012-03-12 22:20:47.000000000 +0100
+++ linux-3.3-rc6-fast/drivers/md/dm-bufio.h 2012-03-12 22:20:50.000000000 +0100
@@ -63,6 +63,14 @@ void *dm_bufio_new(struct dm_bufio_clien
struct dm_buffer **bp);
/*
+ * Prefetch the specified blocks to the cache.
+ * The function starts to read the blocks and returns without waiting for
+ * I/O to finish.
+ */
+void dm_bufio_prefetch(struct dm_bufio_client *c,
+ sector_t block, unsigned n_blocks);
+
+/*
* Release a reference obtained with dm_bufio_{read,get,new}. The data
* pointer and dm_buffer pointer is no longer valid after this call.
*/
--
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