Re: [RFC][PATCH 2/8 v2] ext4: add operations on extent status tree
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From: Theodore Ts'o <tytso@mit.edu>
Date: 2012-09-19 18:35:01
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linux-fsdevel
On Wed, Aug 22, 2012 at 02:05:39PM +0800, Zheng Liu wrote:
quoted hunk ↗ jump to hunk
+ * 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. 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? - Ted