Re: [PATCH 0/3] flush delalloc by multi-task

[Miao Xie <miaox@cn.fujitsu.com>]

On 	thu, 25 Oct 2012 19:53:05 +0800, Liu Bo wrote:
> On 10/25/2012 05:20 PM, Miao Xie wrote:
>> This patchset introduce multi-task delalloc flush, it can make the delalloc
>> flush more faster. And besides that, it also can fix the problem that we join
>> the same transaction handler more than 2 times.
>>
>> Implementation:
>> - Create a new worker pool.
>> - Queue the inode with pending delalloc into the work queue of the worker pool
>>   when we want to force them into the disk, and then we will wait till all the
>>   works we submit are done. 
>> - The ordered extents also can be queued into this work queue. The process is
>>   similar to the second one.
>>
> 
> I can see the potential improvements brought by flushing inodes this way.
> 
> But I don't think it makes much sense by making waiting process multi-task,
> since even we spread wait order extents into different cpus, they just occpied
> the cpu and went on waiting and scheduled then, I mean, the bottleneck is on
> what we're waiting for.

Thanks for your comment, I think only btrfs_run_ordered_operations(root, 0) needn't
wait for the works, the others must wait.

The first reason is to avoid changing the semantic of those tree function. The second
reason is we have to wait for the completion of all works, if not, the file data in
snapshots may be different with the source suvolumes because the flush may not end
before the snapshot creation.

> Besides, considering that this patchset is about to getting us better performance,
> I'm expecting any performance numbers (I'm a little worried about context switches
> overhead).

OK, I'll send it out later.

Thanks
Miao
 
> btw, cool ideas indeed.
> 
> thanks,
> liubo
> 
>> Miao Xie (3):
>>       Btrfs: make delalloc inodes be flushed by multi-task
>>       Btrfs: make ordered operations be handled by multi-task
>>       Btrfs: make ordered extent be flushed by multi-task
>>
>>  fs/btrfs/ctree.h        |   14 +++++++
>>  fs/btrfs/disk-io.c      |    7 ++++
>>  fs/btrfs/inode.c        |   78 ++++++++++++++++++++++++++++++++++++++---
>>  fs/btrfs/ordered-data.c |   87 ++++++++++++++++++++++++++++++++++-------------
>>  fs/btrfs/ordered-data.h |    7 +++-
>>  fs/btrfs/relocation.c   |    6 +++-
>>  fs/btrfs/transaction.c  |   24 ++++++++++---
>>  7 files changed, 185 insertions(+), 38 deletions(-)
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