On Wed, Apr 20, 2022 at 04:30:02PM -0700, Mike Kravetz wrote: > On 4/20/22 10:11, Masahiro Yamada wrote: > > On Wed, Apr 13, 2022 at 11:48 PM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote: > >> > >> If the size of "struct page" is not the power of two but with the feature > >> of minimizing overhead of struct page associated with each HugeTLB is > >> enabled, then the vmemmap pages of HugeTLB will be corrupted after > >> remapping (panic is about to happen in theory). But this only exists when > >> !CONFIG_MEMCG && !CONFIG_SLUB on x86_64. However, it is not a conventional > >> configuration nowadays. So it is not a real word issue, just the result > >> of a code review. But we have to prevent anyone from configuring that > >> combined configurations. In order to avoid many checks like "is_power_of_2 > >> (sizeof(struct page))" through mm/hugetlb_vmemmap.c. Introduce a new macro > > Sorry for jumping in so late. I am far from expert in Kconfig so did not pay > much attention to all those discussions. > > Why not just add one (or a few) simple runtime checks for struct page not a > power of two before enabling hugetlb vmemmap optimization in the code? Sure, > it would be ideal to never build/include the vmemmap optimization code if > this can be detected at config time. However, it seems this is a very rare > combination and the checks for it at config time are very complex. Right. Iterated and explored through 8 versions, I realized checking it at config time is very complex. > Would we really need many checks throughout the code as you mention above? > Or, do we only need to check or two before enabling > hugetlb_optimize_vmemmap_key? Yep, now there is only one place where needs to check that size. I think I should go back to v1, it is simpler. Thanks Mike.
