In order to reduce locking overhead, we introduce a new API: dm_bufio_lock_read, dm_bufio_unlock_read and dm_bufio_get_unlocked.
The user calls dm_bufio_lock_read, then he might call dm_bufio_get_unlocked several times and finally calls dm_bufio_unlock_read. This is intended to simplify btree walks in dm-thin. The follow-up patch will change c->lock from mutex to rw-semaphore, so that there could be multiple processes walking the btree concurently. Signed-off-by: Mikulas Patocka <[email protected]> --- drivers/md/dm-bufio.c | 45 ++++++++++++++++++++++++++++++++++++++------- include/linux/dm-bufio.h | 15 +++++++++++++++ 2 files changed, 53 insertions(+), 7 deletions(-) Index: linux-2.6/drivers/md/dm-bufio.c =================================================================== --- linux-2.6.orig/drivers/md/dm-bufio.c 2022-10-10 11:08:10.000000000 +0200 +++ linux-2.6/drivers/md/dm-bufio.c 2022-10-10 11:13:10.000000000 +0200 @@ -145,7 +145,7 @@ struct dm_buffer { unsigned char list_mode; /* LIST_* */ blk_status_t read_error; blk_status_t write_error; - unsigned accessed; + volatile unsigned accessed; unsigned hold_count; unsigned long state; unsigned long last_accessed; @@ -193,6 +193,18 @@ static void dm_bufio_unlock(struct dm_bu mutex_unlock(&c->lock); } +void dm_bufio_lock_read(struct dm_bufio_client *c) +{ + mutex_lock(&c->lock); +} +EXPORT_SYMBOL_GPL(dm_bufio_lock_read); + +void dm_bufio_unlock_read(struct dm_bufio_client *c) +{ + mutex_unlock(&c->lock); +} +EXPORT_SYMBOL_GPL(dm_bufio_unlock_read); + /*----------------------------------------------------------------*/ /* @@ -870,7 +882,8 @@ enum new_flag { NF_FRESH = 0, NF_READ = 1, NF_GET = 2, - NF_PREFETCH = 3 + NF_GET_UNLOCKED = 3, + NF_PREFETCH = 4 }; /* @@ -1013,7 +1026,7 @@ static struct dm_buffer *__bufio_new(str if (b) goto found_buffer; - if (nf == NF_GET) + if (nf == NF_GET || nf == NF_GET_UNLOCKED) return NULL; new_b = __alloc_buffer_wait(c, nf); @@ -1058,12 +1071,17 @@ found_buffer: * 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))) + if ((nf == NF_GET || nf == NF_GET_UNLOCKED) && 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)); + if (nf == NF_GET_UNLOCKED) { + if (!b->accessed) + b->accessed = 1; + } else { + b->hold_count++; + __relink_lru(b, test_bit(B_DIRTY, &b->state) || + test_bit(B_WRITING, &b->state)); + } return b; } @@ -1154,6 +1172,19 @@ void *dm_bufio_new(struct dm_bufio_clien } EXPORT_SYMBOL_GPL(dm_bufio_new); +void *dm_bufio_get_unlocked(struct dm_bufio_client *c, sector_t block, + struct dm_buffer **bp) +{ + int need_submit; + struct dm_buffer *b = __bufio_new(c, block, NF_GET_UNLOCKED, &need_submit, NULL); + if (b) { + *bp = b; + return b->data; + } + return NULL; +} +EXPORT_SYMBOL_GPL(dm_bufio_get_unlocked); + void dm_bufio_prefetch(struct dm_bufio_client *c, sector_t block, unsigned n_blocks) { Index: linux-2.6/include/linux/dm-bufio.h =================================================================== --- linux-2.6.orig/include/linux/dm-bufio.h 2022-10-10 11:13:10.000000000 +0200 +++ linux-2.6/include/linux/dm-bufio.h 2022-10-10 11:13:25.000000000 +0200 @@ -38,6 +38,13 @@ dm_bufio_client_create(struct block_devi void dm_bufio_client_destroy(struct dm_bufio_client *c); /* + * Lock and unlock the bufio client - this is needed if we want to call + * dm_bufio_get_unlocked. + */ +void dm_bufio_lock_read(struct dm_bufio_client *c); +void dm_bufio_unlock_read(struct dm_bufio_client *c); + +/* * Set the sector range. * When this function is called, there must be no I/O in progress on the bufio * client. @@ -76,6 +83,14 @@ void *dm_bufio_new(struct dm_bufio_clien struct dm_buffer **bp); /* + * Like dm_bufio_get, but assume that the client is already locked with + * dm_bufio_lock_read/dm_bufio_unlock_read. dm_bufio_release should not be + * called; the caller should call dm_bufio_unlock_read to release the buffer. + */ +void *dm_bufio_get_unlocked(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. -- dm-devel mailing list [email protected] https://listman.redhat.com/mailman/listinfo/dm-devel
