On Mon, Aug 27, 2012 at 10:52:20AM -0600, Liu Bo wrote:
> 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@xxxxxxxxxx>
> ---
> fs/btrfs/extent_map.c | 20 ++++++++++++++++++++
> fs/btrfs/extent_map.h | 2 ++
> fs/btrfs/inode.c | 1 +
> fs/btrfs/tree-log.c | 6 +++---
> 4 files changed, 26 insertions(+), 3 deletions(-)
>
> 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 @@ static void try_merge_map(struct extent_map_tree *tree, struct extent_map *em)
> 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;
Shouldn't this be
em->mod_start = merge->start;
em->mod_len += merge_len;
> em->generation = merge->generation;
> list_move(&em->list, &tree->modified_extents);
> }
> @@ -222,6 +224,7 @@ static void try_merge_map(struct extent_map_tree *tree, struct extent_map *em)
> rb_erase(&merge->rb_node, &tree->map);
> merge->in_tree = 0;
> if (merge->generation > em->generation) {
> + em->mod_len = em->len;
And this should be em->mod_len += em->len?
Thanks,
Josef
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