Re: [RFC][PATCH 2/8 v2] ext4: add operations on extent status tree

On Wed, Sep 19, 2012 at 02:34:52PM -0400, Theodore Ts'o wrote:

On Wed, Aug 22, 2012 at 02:05:39PM +0800, Zheng Liu wrote:

quoted

+ * 3. performance analysis
+ *   --	overhead
+ *	1. Apart from operations on a delayed extent tree, we need to
+ *	down_write(inode->i_data_sem) in delayed write path to maintain delayed
+ *	extent tree, this can have impact on parallel read-write and write-write

I'm working on going through this patch set now, and I'm not sure this
is worth holding back on this patch series, but I am really concerned
about the performance impact of this....  it would definitely show up
on some of the scalability testing that Eric Whitney had been doing,
for example.

Sorry, maybe I miss some mails.  Could you please tell me where I can
find Eric's mail.  Thanks.

Given that operations on the delayed extent tree should be fast,
instead of using a mutex, any reason why we can't just add a new
spinlock (I'm not even sure we need a rw_spinlock here) to the
ext4_inode_info structure and use that to serialize operations on the
delayed extent tree?

Thanks for your comment.  I will fix it.

Regards,
Zheng