On 08/28/2012 01:12 AM, Josef Bacik wrote:
> 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....@oracle.com>
>> ---
>> 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;
>
They just do the same thing.
There is already a
em->start = merge->start;
em->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?
>
No, em->len has already contained the merge's len.
thanks,
liubo
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