Re: More OOM problems

[Michal Hocko <mhocko@suse.cz>]

On Mon 19-09-16 07:31:06, Andi Kleen wrote:
> On Mon, Sep 19, 2016 at 08:37:36AM -0500, Christoph Lameter wrote:
> > On Sun, 18 Sep 2016, Andi Kleen wrote:
> > 
> > > > Sounds like SLUB. SLAB would use order-0 as long as things fit. I would
> > > > hope for SLUB to fallback to order-0 (or order-1 for 8kB) instead of
> > > > OOM, though. Guess not...
> > >
> > > It's already trying to do that, perhaps just some flags need to be
> > > changed?
> > 
> > SLUB tries order-N and falls back to order 0 on failure.
> 
> Right it tries, but Linus apparently got an OOM in the order-N
> allocation. So somehow the flag combination that it passes first
> is not preventing the OOM killer.

It does AFAICS:
	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;
	if ((alloc_gfp & __GFP_DIRECT_RECLAIM) && oo_order(oo) > oo_order(s->min))
		alloc_gfp = (alloc_gfp | __GFP_NOMEMALLOC) & ~(__GFP_RECLAIM|__GFP_NOFAIL);

	page = alloc_slab_page(s, alloc_gfp, node, oo);
	if (unlikely(!page)) {
		oo = s->min;
		alloc_gfp = flags;
		/*
		 * Allocation may have failed due to fragmentation.
		 * Try a lower order alloc if possible
		 */
		page = alloc_slab_page(s, alloc_gfp, node, oo);

I think that Linus just see a genuine order-3 request
-- 
Michal Hocko
SUSE Labs

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