Before applying this patch, the task had to reclaim the metadata space
by itself if the metadata space was not enough. And When the task started
the space reclamation, all the other tasks which wanted to reserve the
metadata space were blocked. At some cases, they would be blocked for
a long time, it made the performance fluctuate wildly.
So we introduce the background metadata space reclamation, when the space
is about to be exhausted, we insert a reclaim work into the workqueue, the
worker of the workqueue helps us to reclaim the reserved space at the
background. By this way, the tasks needn't reclaim the space by themselves at
most cases, and even if the tasks have to reclaim the space or are blocked
for the space reclamation, they will get enough space more quickly.
Here is my test result(Tested by sysbench for 3 times):
Memory: 2GB
CPU: 2Cores * 1CPU
Partition: 20GB(SSD)
w/o w
seqwr-512KB-1Thread-2GB 180.08MB/s 178.00MB/s
seqwr-512KB-8Threads-2GB 179.14MB/s 179.25MB/s
seqwr-128KB-1Thread-2GB 186.3MB/s 186.57MB/s
seqwr-128KB-8Threads-2GB 176.05MB/s 183.05MB/s
rndwr-512KB-1Thread-2GB 114.20MB/s 117.42MB/s
rndwr-512KB-8Threads-2GB 129.18MB/s 132.51MB/s
rndwr-128KB-1Thread-2GB 963.94MB/s 1.4058GB/s
rndwr-128KB-8Threads-2GB 1.1950GB/s 1.3787GB/s
The above numbers are the averages.
rndwr: random write test
seqwr: sequential write test
512KB,128KB: the size of each request
1Thread, 8Threads: the number of the test threads
2GB: The total file size
For the last two cases, the ramdom write test just executed 10000 requests
every time we ran the test, so the most data was cached in the page cache,
it is why the random test was faster than the sequential write test. And
besides that, according to our test result, the random write performance
on the kernel without the patch was not stable, it fluctuated between
840MB/s and 1.25GB/s. But after applying the patch, the performance of
the random write was stable.
Signed-off-by: Miao Xie <miaox@xxxxxxxxxxxxxx>
---
fs/btrfs/ctree.h | 6 +++
fs/btrfs/disk-io.c | 3 ++
fs/btrfs/extent-tree.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++-
fs/btrfs/super.c | 1 +
4 files changed, 108 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index f9aeb27..e0d2a3b 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -33,6 +33,7 @@
#include <asm/kmap_types.h>
#include <linux/pagemap.h>
#include <linux/btrfs.h>
+#include <linux/workqueue.h>
#include "extent_io.h"
#include "extent_map.h"
#include "async-thread.h"
@@ -1289,6 +1290,8 @@ struct btrfs_stripe_hash_table {
#define BTRFS_STRIPE_HASH_TABLE_BITS 11
+void btrfs_init_async_reclaim_work(struct work_struct *work);
+
/* fs_info */
struct reloc_control;
struct btrfs_device;
@@ -1655,6 +1658,9 @@ struct btrfs_fs_info {
struct semaphore uuid_tree_rescan_sem;
unsigned int update_uuid_tree_gen:1;
+
+ /* Used to reclaim the metadata space in the background. */
+ struct work_struct async_reclaim_work;
};
/*
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 4c4ed0b..2b49923 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2234,6 +2234,7 @@ int open_ctree(struct super_block *sb,
atomic_set(&fs_info->balance_cancel_req, 0);
fs_info->balance_ctl = NULL;
init_waitqueue_head(&fs_info->balance_wait_q);
+ btrfs_init_async_reclaim_work(&fs_info->async_reclaim_work);
sb->s_blocksize = 4096;
sb->s_blocksize_bits = blksize_bits(4096);
@@ -3579,6 +3580,8 @@ int close_ctree(struct btrfs_root *root)
/* clear out the rbtree of defraggable inodes */
btrfs_cleanup_defrag_inodes(fs_info);
+ cancel_work_sync(&fs_info->async_reclaim_work);
+
if (!(fs_info->sb->s_flags & MS_RDONLY)) {
ret = btrfs_commit_super(root);
if (ret)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 12a5b6d..c122dc7 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4230,6 +4230,98 @@ static int flush_space(struct btrfs_root *root,
return ret;
}
+
+static inline u64
+btrfs_calc_reclaim_metadata_size(struct btrfs_root *root,
+ struct btrfs_space_info *space_info)
+{
+ u64 used;
+ u64 expected;
+ u64 to_reclaim;
+
+ to_reclaim = min_t(u64, num_online_cpus() * 1024 * 1024,
+ 32 * 1024 * 1024);
+ spin_lock(&space_info->lock);
+ if (can_overcommit(root, space_info, to_reclaim,
+ BTRFS_RESERVE_FLUSH_ALL)) {
+ to_reclaim = 0;
+ goto out;
+ }
+
+ used = space_info->bytes_used + space_info->bytes_reserved +
+ space_info->bytes_pinned + space_info->bytes_readonly +
+ space_info->bytes_may_use;
+ if (can_overcommit(root, space_info, 1024 * 1024,
+ BTRFS_RESERVE_FLUSH_ALL))
+ expected = div_factor_fine(space_info->total_bytes, 95);
+ else
+ expected = div_factor_fine(space_info->total_bytes, 90);
+ to_reclaim = used - expected;
+out:
+ spin_unlock(&space_info->lock);
+
+ return to_reclaim;
+}
+
+static inline int need_do_async_reclaim(struct btrfs_space_info *space_info,
+ struct btrfs_fs_info *fs_info, u64 used)
+{
+ return (used >= div_factor_fine(space_info->total_bytes, 95) &&
+ !btrfs_fs_closing(fs_info) &&
+ !test_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state));
+}
+
+static int btrfs_need_do_async_reclaim(struct btrfs_space_info *space_info,
+ struct btrfs_fs_info *fs_info)
+{
+ u64 used;
+
+ spin_lock(&space_info->lock);
+ used = space_info->bytes_used + space_info->bytes_reserved +
+ space_info->bytes_pinned + space_info->bytes_readonly +
+ space_info->bytes_may_use;
+ if (need_do_async_reclaim(space_info, fs_info, used)) {
+ spin_unlock(&space_info->lock);
+ return 1;
+ }
+ spin_unlock(&space_info->lock);
+
+ return 0;
+}
+
+static void btrfs_async_reclaim_metadata_space(struct work_struct *work)
+{
+ struct btrfs_fs_info *fs_info;
+ struct btrfs_space_info *space_info;
+ u64 to_reclaim;
+ int flush_state;
+
+ fs_info = container_of(work, struct btrfs_fs_info, async_reclaim_work);
+ space_info = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);
+
+ to_reclaim = btrfs_calc_reclaim_metadata_size(fs_info->fs_root,
+ space_info);
+ if (!to_reclaim)
+ return;
+
+ flush_state = FLUSH_DELAYED_ITEMS_NR;
+ do {
+ flush_space(fs_info->fs_root, space_info, to_reclaim,
+ to_reclaim, flush_state);
+ flush_state++;
+ if (!btrfs_need_do_async_reclaim(space_info, fs_info))
+ return;
+ } while (flush_state <= COMMIT_TRANS);
+
+ if (btrfs_need_do_async_reclaim(space_info, fs_info))
+ queue_work(system_unbound_wq, work);
+}
+
+void btrfs_init_async_reclaim_work(struct work_struct *work)
+{
+ INIT_WORK(work, btrfs_async_reclaim_metadata_space);
+}
+
/**
* reserve_metadata_bytes - try to reserve bytes from the block_rsv's space
* @root - the root we're allocating for
@@ -4337,8 +4429,13 @@ again:
if (ret && flush != BTRFS_RESERVE_NO_FLUSH) {
flushing = true;
space_info->flush = 1;
+ } else if (!ret && space_info->flags & BTRFS_BLOCK_GROUP_METADATA) {
+ used += orig_bytes;
+ if (need_do_async_reclaim(space_info, root->fs_info, used) &&
+ !work_busy(&root->fs_info->async_reclaim_work))
+ queue_work(system_unbound_wq,
+ &root->fs_info->async_reclaim_work);
}
-
spin_unlock(&space_info->lock);
if (!ret || flush == BTRFS_RESERVE_NO_FLUSH)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 2d8ac1b..fb62c45 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1329,6 +1329,7 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
* this also happens on 'umount -rf' or on shutdown, when
* the filesystem is busy.
*/
+ cancel_work_sync(&fs_info->async_reclaim_work);
/* wait for the uuid_scan task to finish */
down(&fs_info->uuid_tree_rescan_sem);
--
1.8.3.1
--
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