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authorMikulas Patocka <mpatocka@redhat.com>2012-03-28 21:41:29 +0400
committerAlasdair G Kergon <agk@redhat.com>2012-03-28 21:41:29 +0400
commita66cc28f53a7e9679dedb2bc66ddb0e0c6bdd0ee (patch)
tree0d1037562bd8a47f6e9d31d7ed56e24c7aa98c66
parent67e2e2b281812b5caf4923a38aadc6b89e34f064 (diff)
downloadlinux-a66cc28f53a7e9679dedb2bc66ddb0e0c6bdd0ee.tar.xz
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@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
-rw-r--r--drivers/md/dm-bufio.c108
-rw-r--r--drivers/md/dm-bufio.h8
2 files changed, 90 insertions, 26 deletions
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index b6e58c7b6df5..cc06a1e52423 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -578,7 +578,7 @@ static void write_endio(struct bio *bio, int error)
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);
}
@@ -697,13 +697,20 @@ static void __wait_for_free_buffer(struct dm_bufio_client *c)
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;
@@ -726,6 +733,9 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
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);
@@ -743,9 +753,12 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
}
}
-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);
@@ -865,32 +878,23 @@ static struct dm_buffer *__find(struct dm_bufio_client *c, sector_t block)
* 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;
*need_submit = 0;
b = __find(c, block);
- if (b) {
- b->hold_count++;
- __relink_lru(b, test_bit(B_DIRTY, &b->state) ||
- test_bit(B_WRITING, &b->state));
- return b;
- }
+ if (b)
+ goto found_buffer;
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
@@ -899,10 +903,7 @@ static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
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);
@@ -922,6 +923,24 @@ static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
*need_submit = 1;
return 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));
+ return b;
}
/*
@@ -956,10 +975,10 @@ static void *new_read(struct dm_bufio_client *c, sector_t block,
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))
+ if (!b)
return b;
if (need_submit)
@@ -1005,13 +1024,47 @@ void *dm_bufio_new(struct dm_bufio_client *c, sector_t block,
}
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();
+
+ if (!n_blocks)
+ goto flush_plug;
+ dm_bufio_lock(c);
+ }
+
+ }
+
+ dm_bufio_unlock(c);
+
+flush_plug:
+ blk_finish_plug(&plug);
+}
+EXPORT_SYMBOL_GPL(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--;
@@ -1024,6 +1077,7 @@ void dm_bufio_release(struct dm_buffer *b)
* 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);
@@ -1041,6 +1095,8 @@ void dm_bufio_mark_buffer_dirty(struct dm_buffer *b)
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);
diff --git a/drivers/md/dm-bufio.h b/drivers/md/dm-bufio.h
index 5c4c3a04e381..b142946a9e32 100644
--- a/drivers/md/dm-bufio.h
+++ b/drivers/md/dm-bufio.h
@@ -63,6 +63,14 @@ void *dm_bufio_new(struct dm_bufio_client *c, sector_t block,
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.
*/