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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>
This commit is contained in:
Mikulas Patocka 2012-03-28 18:41:29 +01:00 committed by Alasdair G Kergon
parent 67e2e2b281
commit a66cc28f53
2 changed files with 90 additions and 26 deletions
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108
drivers/md/dm-bufio.c
View File

@ -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);

8
drivers/md/dm-bufio.h
View File

@ -62,6 +62,14 @@ void *dm_bufio_get(struct dm_bufio_client *c, sector_t block,
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.