Re: [PATCH v2 2/2] slab: __GFP_ZERO is incompatible with a constructor

[Matthew Wilcox]

On Thu, Apr 12, 2018 at 09:10:23AM -0500, Christopher Lameter wrote:
> On Wed, 11 Apr 2018, Matthew Wilcox wrote:
> > I don't see how that works ... can you explain a little more?
>
> c->freelist is NULL and thus ___slab_alloc (slowpath) is called.
> ___slab_alloc populates c->freelist and gets the new object pointer.
> 
> if debugging is on then c->freelist is set to NULL at the end of
> ___slab_alloc because deactivate_slab() is called.
> 
> Thus the next invocation of the fastpath will find that c->freelist is
> NULL and go to the slowpath. ...

_ah_.  I hadn't figured out that c->page was always NULL in the debugging
case too, so ___slab_alloc() always hits the 'new_slab' case.  Thanks!