Re: [PATCH 1/2] mm/vmap: Add a notifier for when we run out of vmap address space

[Roman Peniaev]

On Thu, Mar 17, 2016 at 1:57 PM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> On Thu, Mar 17, 2016 at 01:37:06PM +0100, Roman Peniaev wrote:
>> > +       freed = 0;
>> > +       blocking_notifier_call_chain(&vmap_notify_list, 0, &freed);
>>
>> It seems to me that alloc_vmap_area() was designed not to sleep,
>> at least on GFP_NOWAIT path (__GFP_DIRECT_RECLAIM is not set).
>>
>> But blocking_notifier_call_chain() might sleep.
>
> Indeed, I had not anticipated anybody using GFP_ATOMIC or equivalently
> restrictive gfp_t for vmap and yes there are such callers.
>
> Would guarding the notifier with gfp & __GFP_DIRECT_RECLAIM and
> !(gfp & __GFP_NORETRY) == be sufficient? Is that enough for GFP_NOFS?

I would use gfpflags_allow_blocking() for that purpose.

Roman