Messages in this thread | | | Date | Fri, 10 Jun 2022 11:57:54 +0800 | Subject | Re: [PATCH] arm64/hugetlb: Simplify the huge_ptep_set_access_flags() | From | Baolin Wang <> |
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On 6/9/2022 11:44 PM, Will Deacon 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. >> >> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> >> --- >> arch/arm64/mm/hugetlbpage.c | 10 +--------- >> 1 file changed, 1 insertion(+), 9 deletions(-) >> >> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c >> index e2a5ec9..5c703aa 100644 >> --- a/arch/arm64/mm/hugetlbpage.c >> +++ b/arch/arm64/mm/hugetlbpage.c >> @@ -448,7 +448,6 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma, >> size_t pgsize = 0; >> unsigned long pfn = pte_pfn(pte), dpfn; >> pgprot_t hugeprot; >> - pte_t orig_pte; >> >> if (!pte_cont(pte)) >> return ptep_set_access_flags(vma, addr, ptep, pte, dirty); >> @@ -459,14 +458,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma, >> if (!__cont_access_flags_changed(ptep, pte, ncontig)) >> return 0; >> >> - orig_pte = get_clear_contig(vma->vm_mm, addr, ptep, pgsize, ncontig); >> - >> - /* Make sure we don't lose the dirty or young state */ >> - if (pte_dirty(orig_pte)) >> - pte = pte_mkdirty(pte); >> - >> - if (pte_young(orig_pte)) >> - pte = pte_mkyoung(pte); >> + clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig); > > I don't understand what this clear_flush() call is doing here; notably, it > includes TLB invalidation which we don't have for the non-cont case.
OK. I can just call a loop of pte_clear() to clear cont-pte to avoid TLB flush.
> > Why isn't huge_ptep_set_access_flags() just a loop around > ptep_set_access_flags() if huge_ptep_get() is taking care of collapsing the > dirty/young state?
IIUC, according to the comments "Changing some bits of contiguous entries requires us to follow a Break-Before-Make approach, breaking the whole contiguous set before we can change any entries". So we should clear the cont-ptes firstly, then re-set them. Then a loop of ptep_set_access_flags() is not suitable for the cont-pte case, right? Please correct me if I missed something else. Thanks.
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