Messages in this thread | | | Date | Sat, 18 Jun 2022 12:17:41 +0800 | Subject | Re: [PATCH] arm64/hugetlb: Simplify the huge_ptep_set_access_flags() | From | Baolin Wang <> |
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On 6/18/2022 1:46 AM, Catalin Marinas wrote: > On Wed, May 25, 2022 at 06:31:09PM +0800, Baolin Wang wrote: >> After commit bc5dfb4fd7bd ("arm64/hugetlb: Implement arm64 specific >> huge_ptep_get()"), the arm64 specific huge_ptep_get() will always >> consider the subpages' dirty and young state for CONT-PTE/PMD hugetlb, >> so there is no need to check them again when setting the access flags >> for CONT-PTE/PMD hugetlb in huge_ptep_set_access_flags(). >> >> Meanwhile this also fixes an issue when users want to make the CONT-PTE/PMD >> hugetlb's pte entry old, which will be failed to make the pte entry old >> since the original code will always consider the subpages' young state >> if the subpages' young state is set. For example, we will make the >> CONT-PTE/PMD hugetlb pte entry old in DAMON to monitoring the accesses, >> but we'll failed to monitoring the actual accesses of the CONT-PTE/PMD >> hugetlb page, due to we can not make its pte old. >> >> Thus remove the code considering the subpages' dirty and young state in >> huge_ptep_set_access_flags() to fix this issue and simplify the function. > > The ptep_set_access_flags() semantics (non-huge) never clear the access > flag, so mkold is not allowed. I think damon_hugetlb_mkold() is wrong in > assuming that huge_ptep_set_access_flags() allows a young->old huge pte > transition.
After reading the code carefully, yes, you are right. Seems I need change to use set_huge_pte_at() to make the huge pte old. Thanks.
By the way, after changing to use set_huge_pte_at() in the damon_hugetlb_mkold(), it seems to me that we still do not need to get the subpages' dirty and young state again in huge_ptep_set_access_flags(). How do you think?
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