Btrfs: improve fsync by filtering extents that we want
This is based on Josef's "Btrfs: turbo charge fsync".
The above Josef's patch performs very good in random sync write test,
because we won't have too much extents to merge.
However, it does not performs good on the test:
dd if=/dev/zero of=foobar bs=4k count=12500 oflag=sync
The reason is when we do sequencial sync write, we need to merge the
current extent just with the previous one, so that we can get accumulated
extents to log:
A(4k) --> AA(8k) --> AAA(12k) --> AAAA(16k) ...
So we'll have to flush more and more checksum into log tree, which is the
bottleneck according to my tests.
But we can avoid this by telling fsync the real extents that are needed
to be logged.
With this, I did the above dd sync write test (size=50m),
w/o (orig) w/ (josef's) w/ (this)
SATA 104KB/s 109KB/s 121KB/s
ramdisk 1.5MB/s 1.5MB/s 10.7MB/s (613%)
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 1fe82cf..ac606f0 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -203,6 +203,8 @@
em->block_start = merge->block_start;
merge->in_tree = 0;
if (merge->generation > em->generation) {
+ em->mod_start = em->start;
+ em->mod_len = em->len;
em->generation = merge->generation;
list_move(&em->list, &tree->modified_extents);
}
@@ -222,6 +224,7 @@
rb_erase(&merge->rb_node, &tree->map);
merge->in_tree = 0;
if (merge->generation > em->generation) {
+ em->mod_len = em->len;
em->generation = merge->generation;
list_move(&em->list, &tree->modified_extents);
}
@@ -247,6 +250,7 @@
{
int ret = 0;
struct extent_map *em;
+ bool prealloc = false;
write_lock(&tree->lock);
em = lookup_extent_mapping(tree, start, len);
@@ -259,8 +263,21 @@
list_move(&em->list, &tree->modified_extents);
em->generation = gen;
clear_bit(EXTENT_FLAG_PINNED, &em->flags);
+ em->mod_start = em->start;
+ em->mod_len = em->len;
+
+ if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) {
+ prealloc = true;
+ clear_bit(EXTENT_FLAG_PREALLOC, &em->flags);
+ }
try_merge_map(tree, em);
+
+ if (prealloc) {
+ em->mod_start = em->start;
+ em->mod_len = em->len;
+ }
+
free_extent_map(em);
out:
write_unlock(&tree->lock);
@@ -298,6 +315,9 @@
}
atomic_inc(&em->refs);
+ em->mod_start = em->start;
+ em->mod_len = em->len;
+
try_merge_map(tree, em);
out:
return ret;
diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
index 2388a60..8e6294b 100644
--- a/fs/btrfs/extent_map.h
+++ b/fs/btrfs/extent_map.h
@@ -20,6 +20,8 @@
/* all of these are in bytes */
u64 start;
u64 len;
+ u64 mod_start;
+ u64 mod_len;
u64 orig_start;
u64 block_start;
u64 block_len;
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ca4fa05..878116d 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1308,6 +1308,7 @@
em->block_start = disk_bytenr;
em->bdev = root->fs_info->fs_devices->latest_bdev;
set_bit(EXTENT_FLAG_PINNED, &em->flags);
+ set_bit(EXTENT_FLAG_PREALLOC, &em->flags);
while (1) {
write_lock(&em_tree->lock);
ret = add_extent_mapping(em_tree, em);
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 58075d7..71e7153 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2833,8 +2833,8 @@
struct btrfs_root *log = root->log_root;
struct btrfs_file_extent_item *fi;
struct btrfs_key key;
- u64 start = em->start;
- u64 len = em->len;
+ u64 start = em->mod_start;
+ u64 len = em->mod_len;
u64 num_bytes;
int nritems;
int ret;
@@ -2970,7 +2970,7 @@
* sequential then we need to copy the items we have and redo
* our search
*/
- if (args.nr && em->start != args.next_offset) {
+ if (args.nr && em->mod_start != args.next_offset) {
ret = copy_items(trans, log, dst_path, args.src,
args.start_slot, args.nr,
LOG_INODE_ALL);
