Re: [PATCH v4 2/2] mm: avoid slub allocation while holding list_lock

[Christopher Lameter]

On Sun, 10 Nov 2019, Yu Zhao wrote:

> On Sat, Nov 09, 2019 at 11:16:28PM +0000, Christopher Lameter wrote:
> > On Sat, 9 Nov 2019, Yu Zhao wrote:
> >
> > > >  	struct page *page, *h;
> > > > +	unsigned long *map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL);
> > > > +
> > > > +	if (!map)
> > > > +		return;
> > >
> > > What would happen if we are trying to allocate from the slab that is
> > > being shut down? And shouldn't the allocation be conditional (i.e.,
> > > only when CONFIG_SLUB_DEBUG=y)?
> >
> > Kmalloc slabs are never shut down.
>
> Maybe I'm not thinking straight -- isn't it what caused the deadlock in
> the first place?

Well if kmalloc allocations become a problem then we have numerous
issues all over the kernel to fix.

> Kmalloc slabs can be shut down when memcg is on.

Kmalloc needs to work even during shutdown of a memcg.

Maybe we need to fix memcg to not allocate from the current memcg during
shutdown?