On Thu, Feb 11, 2021 at 04:19:55PM -0800, Mike Kravetz wrote: > want_pmd_share() is currently just a check for > CONFIG_ARCH_WANT_HUGE_PMD_SHARE. > How about leaving that mostly as is, and adding the new vma checks to > vma_shareable(). vma_shareable() would then be something like: > > if (!(vma->vm_flags & VM_MAYSHARE)) > return false; > #ifdef CONFIG_USERFAULTFD > if (uffd_disable_huge_pmd_share(vma) > return false; > #endif > #ifdef /* XXX */ > /* add other checks for things like uffd wp and soft dirty here */ > #endif /* XXX */ > > if (range_in_vma(vma, base, end) > return true; > return false; > > Of course, this would require we leave the call to vma_shareable() at the > beginning of huge_pmd_share. It also means that we are always making a > function call into huge_pmd_share to determine if sharing is possible. > That is not any different than today. If we do not want to make that extra > function call, then I would suggest putting all that code in want_pmd_share. > It just seems that all the vma checks for sharing should be in one place > if possible.
I don't worry a lot on that since we've already got huge_pte_alloc() which takes care of huge pmd sharing case, so I don't expect e.g. even most hugetlb developers to use want_pmd_share() at all, because huge_pte_alloc() will be the one that frequently got called. But yeah we can definitely put the check logic into huge_pmd_share() too. Looking at above code it looks still worth a helper like want_pmd_share() or with some other name. Then... instead of making this complicated, how about I mostly keep this patch but move want_pmd_share() call into huge_pmd_share() instead? Btw, Axel, it seems there will still be some respins on the pmd sharing patches. Since it turns out it'll be shared by multiple tasks now, do you mind I pick those out and send them separately? Then we can consolidate this part to move on with either the rest of the tasks we've got on hand. Thanks, -- Peter Xu
