Hi Regarding that dm-bufio overhead, I created this patch.
The patch exports dm_bufio_lock, dm_bufio_trylock and dm_bufio_unlock and introduces a new function dm_bufio_get_unlocked. dm_bufio_get_unlocked is like dm_bufio_get, except that it doesn't take the lock and it assumes that the client structure is already locked with dm_bufio_lock. When you walk the thinp metadata, it is recommended that you call dm_bufio_lock, then you call dm_bufio_get_unlocked repeatedly for each b-tree level and finally you call dm_bufio_unlock. So, you can walk the b-tree with just one lock/unlock pair. When dm_bufio_get_unlocked returns NULL (the block is not in cache), you must call dm_bufio_unlock and then read the data with dm_bufio_read as usual - in this situation, the I/O will be bottleneck rather than locking. Mikulas Signed-off-by: Mikulas Patocka <[email protected]> --- drivers/md/dm-bufio.c | 29 ++++++++++++++++++++++------- include/linux/dm-bufio.h | 15 +++++++++++++++ 2 files changed, 37 insertions(+), 7 deletions(-) Index: linux-dm/drivers/md/dm-bufio.c =================================================================== --- linux-dm.orig/drivers/md/dm-bufio.c 2022-09-05 13:29:52.000000000 +0200 +++ linux-dm/drivers/md/dm-bufio.c 2022-09-27 15:43:18.000000000 +0200 @@ -169,29 +169,32 @@ static DEFINE_STATIC_KEY_FALSE(no_sleep_ #define dm_bufio_in_request() (!!current->bio_list) -static void dm_bufio_lock(struct dm_bufio_client *c) +void dm_bufio_lock(struct dm_bufio_client *c) { if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep) spin_lock_bh(&c->spinlock); else mutex_lock_nested(&c->lock, dm_bufio_in_request()); } +EXPORT_SYMBOL_GPL(dm_bufio_lock); -static int dm_bufio_trylock(struct dm_bufio_client *c) +int dm_bufio_trylock(struct dm_bufio_client *c) { if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep) return spin_trylock_bh(&c->spinlock); else return mutex_trylock(&c->lock); } +EXPORT_SYMBOL_GPL(dm_bufio_trylock); -static void dm_bufio_unlock(struct dm_bufio_client *c) +void dm_bufio_unlock(struct dm_bufio_client *c) { if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep) spin_unlock_bh(&c->spinlock); else mutex_unlock(&c->lock); } +EXPORT_SYMBOL_GPL(dm_bufio_unlock); /*----------------------------------------------------------------*/ @@ -870,7 +873,8 @@ enum new_flag { NF_FRESH = 0, NF_READ = 1, NF_GET = 2, - NF_PREFETCH = 3 + NF_GET_UNLOCKED = 3, + NF_PREFETCH = 4 }; /* @@ -1013,7 +1017,7 @@ 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); @@ -1058,10 +1062,11 @@ 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++; + b->hold_count += nf != NF_GET_UNLOCKED; + __relink_lru(b, test_bit(B_DIRTY, &b->state) || test_bit(B_WRITING, &b->state)); return b; @@ -1154,6 +1159,16 @@ 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) +{ + int need_submit; + struct dm_buffer *b = __bufio_new(c, block, NF_GET_UNLOCKED, &need_submit, NULL); + if (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-dm/include/linux/dm-bufio.h =================================================================== --- linux-dm.orig/include/linux/dm-bufio.h 2022-09-05 13:29:56.000000000 +0200 +++ linux-dm/include/linux/dm-bufio.h 2022-09-27 15:36:49.000000000 +0200 @@ -38,6 +38,14 @@ 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(struct dm_bufio_client *c); +int dm_bufio_trylock(struct dm_bufio_client *c); +void dm_bufio_unlock(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 +84,13 @@ 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/dm_bufio_unlock. dm_bufio_release should not be called; + * the caller should call dm_bufio_unlock to release the buffer. + */ +void *dm_bufio_get_unlocked(struct dm_bufio_client *c, sector_t block); + +/* * 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
