RE: [PATCH v20 0/7] Virtio-balloon Enhancement
From: Wang, Wei W
Date: Wed Dec 20 2017 - 11:13:29 EST
On Wednesday, December 20, 2017 8:26 PM, Matthew Wilcox wrote:
> On Wed, Dec 20, 2017 at 06:34:36PM +0800, Wei Wang wrote:
> > On 12/19/2017 10:05 PM, Tetsuo Handa wrote:
> > > I think xb_find_set() has a bug in !node path.
> > I think we can probably remove the "!node" path for now. It would be
> > good to get the fundamental part in first, and leave optimization to
> > come as separate patches with corresponding test cases in the future.
> You can't remove the !node path. You'll see !node when the highest set bit
> is less than 1024. So do something like this:
> unsigned long bit;
> xb_set_bit(xb, 700);
> bit = xb_find_set(xb, ULONG_MAX, 0);
> assert(bit == 700);
This above test will result in "!node with bitmap !=NULL", and it goes to the regular "if (bitmap)" path, which finds 700.
A better test would be
assert(xb_find_set(xb, ULONG_MAX, 800) == ULONG_MAX);
The first try with the "if (bitmap)" path doesn't find a set bit, and the remaining tries will always result in "!node && !bitmap", which implies no set bit anymore and no need to try in this case.
So, I think we can change it to
If (!node && !bitmap)