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I don't think they'll be terribly intrusive or risky? > > > > I will start on adding follow_huge_pgd() support. Although, I may need > > some help with verification from the powerpc folks, as that is the only > > architecture which supports hugetlb pages at that level. > > > > mpe any suggestions? > > I'm happy to test. > > I have a system where I can allocate 1GB huge pages. > > I'm not sure how to actually test this path though. I hacked up the > vm/migration.c test to allocate 1GB hugepages, but I can't see it going > through follow_huge_pgd() (using ftrace). I thing you needed to use 16GB to trigger this code path. Anshuman introduced support for page offline (and migration) at this level in commit 94310cbcaa3c ("mm/madvise: enable (soft|hard) offline of HugeTLB pages at PGD level"). When asked about the use case, he mentioned: "Yes, its in the context of 16GB pages on POWER8 system where all the gigantic pages are pre allocated from the platform and passed on to the kernel through the device tree. We dont allocate these gigantic pages on runtime." -- Mike Kravetz > > Maybe I hacked it up badly, I'll have a closer look on Monday. But if > you have any tips on how to trigger that path let me know :) > > cheers