Messages in this thread | | | Date | Tue, 05 May 2015 11:12:52 +0200 | From | Vlastimil Babka <> | Subject | Re: [patch v2 for-4.0] mm, thp: really limit transparent hugepage allocation to local node |
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On 04/21/2015 09:31 AM, Aneesh Kumar K.V wrote: > Vlastimil Babka <vbabka@suse.cz> writes: > >> On 25.2.2015 22:24, David Rientjes wrote: >>> >>>> alloc_pages_preferred_node() variant, change the exact_node() variant to pass >>>> __GFP_THISNODE, and audit and adjust all callers accordingly. >>>> >>> Sounds like that should be done as part of a cleanup after the 4.0 issues >>> are addressed. alloc_pages_exact_node() does seem to suggest that we want >>> exactly that node, implying __GFP_THISNODE behavior already, so it would >>> be good to avoid having this come up again in the future. >> >> Oh lovely, just found out that there's alloc_pages_node which should be the >> preferred-only version, but in fact does not differ from >> alloc_pages_exact_node >> in any relevant way. I agree we should do some larger cleanup for next >> version. >> >>>> Also, you pass __GFP_NOWARN but that should be covered by GFP_TRANSHUGE >>>> already. Of course, nothing guarantees that hugepage == true implies that gfp >>>> == GFP_TRANSHUGE... but current in-tree callers conform to that. >>>> >>> Ah, good point, and it includes __GFP_NORETRY as well which means that >>> this patch is busted. It won't try compaction or direct reclaim in the >>> page allocator slowpath because of this: >>> >>> /* >>> * GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and >>> * __GFP_NOWARN set) should not cause reclaim since the subsystem >>> * (f.e. slab) using GFP_THISNODE may choose to trigger reclaim >>> * using a larger set of nodes after it has established that the >>> * allowed per node queues are empty and that nodes are >>> * over allocated. >>> */ >>> if (IS_ENABLED(CONFIG_NUMA) && >>> (gfp_mask & GFP_THISNODE) == GFP_THISNODE) >>> goto nopage; >>> >>> Hmm. It would be disappointing to have to pass the nodemask of the exact >>> node that we want to allocate from into the page allocator to avoid using >>> __GFP_THISNODE. >> >> Yeah. >> >>> >>> There's a sneaky way around it by just removing __GFP_NORETRY from >>> GFP_TRANSHUGE so the condition above fails and since the page allocator >>> won't retry for such a high-order allocation, but that probably just >>> papers over this stuff too much already. I think what we want to do is >> >> Alternatively alloc_pages_exact_node() adds __GFP_THISNODE just to >> node_zonelist() call and not to __alloc_pages() gfp_mask proper? Unless >> __GFP_THISNODE >> was given *also* in the incoming gfp_mask, this should give us the right >> combination? >> But it's also subtle.... >> >>> cause the slab allocators to not use __GFP_WAIT if they want to avoid >>> reclaim. >> >> Yes, the fewer subtle heuristics we have that include combinations of >> flags (*cough* >> GFP_TRANSHUGE *cough*), the better. >> >>> This is probably going to be a much more invasive patch than originally >>> thought. >> >> Right, we might be changing behavior not just for slab allocators, but >> also others using such >> combination of flags. > > Any update on this ? Did we reach a conclusion on how to go forward here > ?
I believe David's later version was merged already. Or what exactly are you asking about?
> -aneesh >
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