[dm-devel] [PATCH 4/4 v2] persistent-data: reduce lock contention while walking the btree
Mikulas Patocka
mpatocka at redhat.com
Tue Oct 11 19:10:19 UTC 2022
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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