Re: [dm-devel] [PATCH 1 of 2] DM Snapshot: remove redundant valid test

[Alasdair G Kergon <agk redhat com>]

On Wed, Sep 23, 2009 at 10:19:08AM -0500, Jon Brassow wrote:
> Patch name: dm-snapshot-remove-redundant-valid-test.patch
> There is another valid test when we take the lock, the previous test can
> be dropped.
 
I'm going to leave this one for now, until I've seen the performance analysis.
- Is the argument here that the gain from not checking it twice while the snapshot
is valid outweighs the cost of the extra locking when the snapshot is full and
pending I/O is being failed as rapidly as possible and by that time there'll be
no other threads fighting for that lock?

Alasdair