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

[Michael S. Tsirkin]

On Sat, Dec 16, 2017 at 01:21:52AM +0900, Tetsuo Handa wrote:
> My understanding is that virtio-balloon wants to handle sparsely spreaded
> unsigned long values (which is PATCH 4/7) and wants to find all chunks of
> consecutive "1" bits efficiently. Therefore, I guess that holding the values
> in ascending order at store time is faster than sorting the values at read
> time.

Are you asking why is a bitmap used here, as opposed to a tree?  It's
not just store versus read. There's also the issue that memory can get
highly fragmented, if it is, the number of 1s is potentially very high.
A bitmap can use as little as 1 bit per value, it is hard to beat in
this respect.

-- 
MST