On Fri, 23 May 2014, Marcelo Tosatti wrote: > Zone specific allocations, such as GFP_DMA32, should not be restricted > to cpusets allowed node list: the zones which such allocations demand > might be contained in particular nodes outside the cpuset node list. > > The alternative would be to not perform such allocations from > applications which are cpuset restricted, which is unrealistic. >
Or ensure applications that allocate from lowmem are allowed to do so, but I understand that might be hard to make sure always happens. > Fixes KVM's alloc_page(gfp_mask=GFP_DMA32) with cpuset as explained. > > Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 5dba293..f228039 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2698,6 +2698,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int > order, > unsigned int cpuset_mems_cookie; > int alloc_flags = ALLOC_WMARK_LOW|ALLOC_CPUSET|ALLOC_FAIR; > struct mem_cgroup *memcg = NULL; > + nodemask_t *cpuset_mems_allowed = &cpuset_current_mems_allowed; > > gfp_mask &= gfp_allowed_mask; > > @@ -2726,9 +2727,14 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int > order, > retry_cpuset: > cpuset_mems_cookie = read_mems_allowed_begin(); > > +#ifdef CONFIG_NUMA > + if (gfp_zone(gfp_mask) < policy_zone) > + cpuset_mems_allowed = NULL; > +#endif > + > /* The preferred zone is used for statistics later */ > first_zones_zonelist(zonelist, high_zoneidx, > - nodemask ? : &cpuset_current_mems_allowed, > + nodemask ? : cpuset_mems_allowed, > &preferred_zone); > if (!preferred_zone) > goto out; > I think this is incomplete. Correct me if I'm wrong on how this is working: preferred_zone, today, is NULL because first_zones_zonelist() is restricted to a cpuset.mems that does not include lowmem and your patch fixes that. But if the fastpath allocation with mandatory ALLOC_CPUSET fails and we go to the slowpath, which may or may not have showed up in your testing, there's still issues, particularly if __GFP_WAIT and lots of allocators do GFP_KERNEL | __GFP_DMA32. This requires ALLOC_CPUSET on all allocations and you haven't updated __cpuset_node_allowed_softwall() with this exception nor zlc_setup(). After that's done, I think all of this is really convoluted and deserves a comment to describe the ALLOC_CPUSET and __GFP_DMA32 behavior. Adding Li, the cpusets maintainer, to this as well. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
