Re: [PATCH v2 3/3] percpu: improve allocation success rate for non-GFP_KERNEL callers

[Michal Hocko]

On Mon 27-02-17 18:07:53, Michal Hocko wrote:
> On Mon 27-02-17 09:01:09, Tahsin Erdogan wrote:
> > On Mon, Feb 27, 2017 at 7:25 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> > >         /*
> > >          * No space left.  Create a new chunk.  We don't want multiple
> > >          * tasks to create chunks simultaneously.  Serialize and create iff
> > >          * there's still no empty chunk after grabbing the mutex.
> > >          */
> > >         if (is_atomic)
> > >                 goto fail;
> > >
> > > right before pcpu_populate_chunk so is this actually a problem?
> > 
> > Yes, this prevents adding more pcpu chunks and so cause "atomic" allocations
> > to fail more easily.
> 
> Then I fail to see what is the problem you are trying to fix.

To be more specific. Could you describe what more can we do in the
vmalloc layer for GFP_NOWAIT allocations? They certainly cannot sleep
and cannot perform the reclaim so you have to rely on the background
work.
-- 
Michal Hocko
SUSE Labs