[dm-devel] [PATCH 4/4 v2] persistent-data: reduce lock contention while walking the btree
Joe Thornber
thornber at redhat.com
Wed Oct 12 06:31:09 UTC 2022
Thanks Mikulas,
I'll test this morning.
- Joe
On Tue, Oct 11, 2022 at 8:10 PM Mikulas Patocka <mpatocka at redhat.com> wrote:
> Hi
>
> Here I'm sending updated patch 4 that fixes hang on discard. We must not
> do the optimization in dm_btree_lookup_next.
>
> Mikulas
>
>
> From: Mikulas Patocka <mpatocka at redhat.com>
>
> This patch reduces lock contention in btree walks. We modify the
> functions init_ro_wpin, exit_ro_spine and ro_step so that they use
> dm_bufio_lock_read/dm_bufio_get_unlocked/dm_bufio_unlock_read. If
> dm_bm_fast_get_block fails, we fallback to normal locking.
>
> When doing tests on pmem and fully provisioned thin volume, it improves
> thoughput from 286MiB/s to 442MiB/s.
>
> fio --ioengine=psync --iodepth=1 --rw=randrw --bs=4k --direct=1
> --numjobs=12 --time_based --runtime=10 --group_reporting --name=/dev/vg/thin
> before:
> READ: bw=286MiB/s
> WRITE: bw=286MiB/s
> after:
> READ: bw=442MiB/s
> WRITE: bw=442MiB/s
>
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
>
> ---
> drivers/md/persistent-data/dm-block-manager.c | 32 +++++++++++++++
> drivers/md/persistent-data/dm-block-manager.h | 6 ++
> drivers/md/persistent-data/dm-btree-internal.h | 4 +
> drivers/md/persistent-data/dm-btree-spine.c | 41
> ++++++++++++++++++--
> drivers/md/persistent-data/dm-btree.c | 6 +-
> drivers/md/persistent-data/dm-transaction-manager.c | 17 ++++++++
> drivers/md/persistent-data/dm-transaction-manager.h | 6 ++
> 7 files changed, 104 insertions(+), 8 deletions(-)
>
> Index: linux-2.6/drivers/md/persistent-data/dm-block-manager.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/persistent-data/dm-block-manager.c
> +++ linux-2.6/drivers/md/persistent-data/dm-block-manager.c
> @@ -601,6 +601,38 @@ void dm_bm_unlock(struct dm_block *b)
> }
> EXPORT_SYMBOL_GPL(dm_bm_unlock);
>
> +void dm_bm_fast_lock(struct dm_block_manager *bm)
> +{
> + dm_bufio_lock_read(bm->bufio);
> +}
> +
> +void dm_bm_fast_unlock(struct dm_block_manager *bm)
> +{
> + dm_bufio_unlock_read(bm->bufio);
> +}
> +
> +int dm_bm_fast_get_block(struct dm_block_manager *bm,
> + dm_block_t b, struct dm_block_validator *v,
> + struct dm_block **result)
> +{
> + int r;
> + struct buffer_aux *aux;
> + void *p;
> +
> + p = dm_bufio_get_unlocked(bm->bufio, b, (struct dm_buffer **)
> result);
> + if (IS_ERR(p))
> + return PTR_ERR(p);
> + if (unlikely(!p))
> + return -EWOULDBLOCK;
> +
> + aux = dm_bufio_get_aux_data(to_buffer(*result));
> + r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
> + if (unlikely(r))
> + return r;
> +
> + return 0;
> +}
> +
> int dm_bm_flush(struct dm_block_manager *bm)
> {
> if (dm_bm_is_read_only(bm))
> Index: linux-2.6/drivers/md/persistent-data/dm-block-manager.h
> ===================================================================
> --- linux-2.6.orig/drivers/md/persistent-data/dm-block-manager.h
> +++ linux-2.6/drivers/md/persistent-data/dm-block-manager.h
> @@ -96,6 +96,12 @@ int dm_bm_write_lock_zero(struct dm_bloc
>
> void dm_bm_unlock(struct dm_block *b);
>
> +void dm_bm_fast_lock(struct dm_block_manager *bm);
> +void dm_bm_fast_unlock(struct dm_block_manager *bm);
> +int dm_bm_fast_get_block(struct dm_block_manager *bm,
> + dm_block_t b, struct dm_block_validator *v,
> + struct dm_block **result);
> +
> /*
> * It's a common idiom to have a superblock that should be committed last.
> *
> Index: linux-2.6/drivers/md/persistent-data/dm-btree-internal.h
> ===================================================================
> --- linux-2.6.orig/drivers/md/persistent-data/dm-btree-internal.h
> +++ linux-2.6/drivers/md/persistent-data/dm-btree-internal.h
> @@ -64,9 +64,11 @@ struct ro_spine {
> struct dm_btree_info *info;
>
> struct dm_block *node;
> + bool fast_locked;
> + bool fast_lock_failed;
> };
>
> -void init_ro_spine(struct ro_spine *s, struct dm_btree_info *info);
> +void init_ro_spine(struct ro_spine *s, struct dm_btree_info *info, bool
> disable_fast_access);
> void exit_ro_spine(struct ro_spine *s);
> int ro_step(struct ro_spine *s, dm_block_t new_child);
> struct btree_node *ro_node(struct ro_spine *s);
> Index: linux-2.6/drivers/md/persistent-data/dm-btree-spine.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/persistent-data/dm-btree-spine.c
> +++ linux-2.6/drivers/md/persistent-data/dm-btree-spine.c
> @@ -118,27 +118,60 @@ void unlock_block(struct dm_btree_info *
> dm_tm_unlock(info->tm, b);
> }
>
> +static void bn_fast_lock(struct dm_btree_info *info)
> +{
> + dm_tm_fast_lock(info->tm);
> +}
> +
> +static void bn_fast_unlock(struct dm_btree_info *info)
> +{
> + dm_tm_fast_unlock(info->tm);
> +}
> +
> +static int bn_fast_get_block(struct dm_btree_info *info, dm_block_t b,
> + struct dm_block **result)
> +{
> + return dm_tm_fast_get_block(info->tm, b, &btree_node_validator,
> result);
> +}
> +
> /*----------------------------------------------------------------*/
>
> -void init_ro_spine(struct ro_spine *s, struct dm_btree_info *info)
> +void init_ro_spine(struct ro_spine *s, struct dm_btree_info *info, bool
> disable_fast_access)
> {
> s->info = info;
> s->node = NULL;
> + s->fast_locked = false;
> + s->fast_lock_failed = disable_fast_access;
> }
>
> void exit_ro_spine(struct ro_spine *s)
> {
> - if (s->node)
> + if (s->fast_locked)
> + bn_fast_unlock(s->info);
> + else if (s->node)
> unlock_block(s->info, s->node);
> }
>
> int ro_step(struct ro_spine *s, dm_block_t new_child)
> {
> if (s->node) {
> - unlock_block(s->info, s->node);
> + if (unlikely(!s->fast_locked))
> + unlock_block(s->info, s->node);
> s->node = NULL;
> }
> -
> + if (likely(!s->fast_lock_failed)) {
> + int r;
> + if (!s->fast_locked) {
> + bn_fast_lock(s->info);
> + s->fast_locked = true;
> + }
> + r = bn_fast_get_block(s->info, new_child, &s->node);
> + if (likely(!r))
> + return 0;
> + s->fast_lock_failed = true;
> + s->fast_locked = false;
> + bn_fast_unlock(s->info);
> + }
> return bn_read_lock(s->info, new_child, &s->node);
> }
>
> Index: linux-2.6/drivers/md/persistent-data/dm-transaction-manager.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/persistent-data/dm-transaction-manager.c
> +++ linux-2.6/drivers/md/persistent-data/dm-transaction-manager.c
> @@ -348,6 +348,23 @@ void dm_tm_unlock(struct dm_transaction_
> }
> EXPORT_SYMBOL_GPL(dm_tm_unlock);
>
> +void dm_tm_fast_lock(struct dm_transaction_manager *tm)
> +{
> + dm_bm_fast_lock(tm->is_clone ? tm->real->bm : tm->bm);
> +}
> +
> +void dm_tm_fast_unlock(struct dm_transaction_manager *tm)
> +{
> + dm_bm_fast_unlock(tm->is_clone ? tm->real->bm : tm->bm);
> +}
> +
> +int dm_tm_fast_get_block(struct dm_transaction_manager *tm, dm_block_t b,
> + struct dm_block_validator *v,
> + struct dm_block **blk)
> +{
> + return dm_bm_fast_get_block(tm->is_clone ? tm->real->bm : tm->bm,
> b, v, blk);
> +}
> +
> void dm_tm_inc(struct dm_transaction_manager *tm, dm_block_t b)
> {
> /*
> Index: linux-2.6/drivers/md/persistent-data/dm-transaction-manager.h
> ===================================================================
> --- linux-2.6.orig/drivers/md/persistent-data/dm-transaction-manager.h
> +++ linux-2.6/drivers/md/persistent-data/dm-transaction-manager.h
> @@ -96,6 +96,12 @@ int dm_tm_read_lock(struct dm_transactio
>
> void dm_tm_unlock(struct dm_transaction_manager *tm, struct dm_block *b);
>
> +void dm_tm_fast_lock(struct dm_transaction_manager *tm);
> +void dm_tm_fast_unlock(struct dm_transaction_manager *tm);
> +int dm_tm_fast_get_block(struct dm_transaction_manager *tm, dm_block_t b,
> + struct dm_block_validator *v,
> + struct dm_block **blk);
> +
> /*
> * Functions for altering the reference count of a block directly.
> */
> Index: linux-2.6/drivers/md/persistent-data/dm-btree.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/persistent-data/dm-btree.c
> +++ linux-2.6/drivers/md/persistent-data/dm-btree.c
> @@ -377,7 +377,7 @@ int dm_btree_lookup(struct dm_btree_info
> __le64 internal_value_le;
> struct ro_spine spine;
>
> - init_ro_spine(&spine, info);
> + init_ro_spine(&spine, info, false);
> for (level = 0; level < info->levels; level++) {
> size_t size;
> void *value_p;
> @@ -472,7 +472,7 @@ int dm_btree_lookup_next(struct dm_btree
> __le64 internal_value_le;
> struct ro_spine spine;
>
> - init_ro_spine(&spine, info);
> + init_ro_spine(&spine, info, true);
> for (level = 0; level < info->levels - 1u; level++) {
> r = btree_lookup_raw(&spine, root, keys[level],
> lower_bound, rkey,
> @@ -1369,7 +1369,7 @@ static int dm_btree_find_key(struct dm_b
> int r = 0, count = 0, level;
> struct ro_spine spine;
>
> - init_ro_spine(&spine, info);
> + init_ro_spine(&spine, info, false);
> for (level = 0; level < info->levels; level++) {
> r = find_key(&spine, root, find_highest, result_keys +
> level,
> level == info->levels - 1 ? NULL : &root);
>
>
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