Messages in this thread | | | Date | Fri, 5 Aug 2005 18:47:03 +0200 | From | Andi Kleen <> | Subject | Re: [RFC] Demand faulting for large pages |
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On Fri, Aug 05, 2005 at 11:37:27AM -0500, Adam Litke wrote: > On Fri, 2005-08-05 at 10:53, Andi Kleen wrote: > > On Fri, Aug 05, 2005 at 10:21:38AM -0500, Adam Litke wrote: > > > Below is a patch to implement demand faulting for huge pages. The main > > > motivation for changing from prefaulting to demand faulting is so that > > > huge page allocations can follow the NUMA API. Currently, huge pages > > > are allocated round-robin from all NUMA nodes. > > > > I think matching DEFAULT is better than having a different default for > > huge pages than for small pages. > > I am not exactly sure what the above means. Is 'DEFAULT' a system > default numa allocation policy?
It's one of the four numa policies: DEFAULT, PREFERED, INTERLEAVE, BIND
It just means allocate on the local node if possible, otherwise fall back.
You said you wanted INTERLEAVE by default, which i think is a bad idea. It should be only optional like in all other allocations.
> > > patch just moves the logic from hugelb_prefault() to > > > hugetlb_pte_fault(). > > > > Are you sure you fixed get_user_pages to handle this properly? It doesn't > > like it. > > Unless I am missing something, the call to follow_hugetlb_page() in > get_user_pages() is just an optimization. Removing it means > follow_page() will be called individually for each PAGE_SIZE page in the > huge page. We can probably do better but I didn't want to cloud this > patch with that logic.
The problem is that get_user_pages needs to handle the case of a large page not yet being faulted in properly. The SLES9 implementation did some changes for this.
You don't change it at all, so I'm suspect it doesn't work yet.
It's a common case - think people doing raw IO on huge pages shared memory.
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