Re: [PATCH v19 3/7] xbitmap: add more operations

On Wed, Dec 13, 2017 at 08:26:06PM +0800, Wei Wang wrote:

On 12/12/2017 09:20 PM, Tetsuo Handa wrote:

quoted

Can you eliminate exception path and fold all xbitmap patches into one, and
post only one xbitmap patch without virtio-baloon changes? If exception path
is valuable, you can add exception path after minimum version is merged.
This series is too difficult for me to close corner cases.

That exception path is claimed to save memory, and I don't have a strong
reason to remove that part.
Matthew, could we get your feedback on this?

Sure.  This code is derived from the IDA code in lib/idr.c.  Eventually,
I intend to reunite them.  For IDA, it clearly makes sense; the first 62
entries result in allocating no memory at all, which is going to be 99%
of users.  After that, we allocate 128 bytes which will serve the first
1024 users.

The xbitmap, as used by Wei's patches here is going to be used somewhat
differently from that.  I understand why Tetsuo wants the exceptional
path removed; I'm not sure the gains will be as important.  But if we're
going to rebuild the IDA on top of the xbitmap, we need to keep them.

I really want to pay more attention to this, but I need to focus on
getting the XArray finished.