Messages in this thread | | | From | Song Liu <> | Subject | Re: [PATCH v2 1/2] khugepaged: enable collapse pmd for pte-mapped THP | Date | Thu, 1 Aug 2019 17:37:03 +0000 |
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> On Aug 1, 2019, at 7:50 AM, Oleg Nesterov <oleg@redhat.com> wrote: > > On 07/31, Song Liu wrote: >> >> +static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm, >> + unsigned long addr) >> +{ >> + struct mm_slot *mm_slot; >> + int ret = 0; >> + >> + /* hold mmap_sem for khugepaged_test_exit() */ >> + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm); >> + VM_BUG_ON(addr & ~HPAGE_PMD_MASK); >> + >> + if (unlikely(khugepaged_test_exit(mm))) >> + return 0; >> + >> + if (!test_bit(MMF_VM_HUGEPAGE, &mm->flags) && >> + !test_bit(MMF_DISABLE_THP, &mm->flags)) { >> + ret = __khugepaged_enter(mm); >> + if (ret) >> + return ret; >> + } > > could you explain why do we need mm->mmap_sem, khugepaged_test_exit() check > and __khugepaged_enter() ?
If the mm doesn't have a mm_slot, we would like to create one here (by calling __khugepaged_enter()).
This happens when the THP is created by another mm, or by tmpfs with "huge=always"; and then page table of this mm got split by split_huge_pmd(). With current kernel, this happens when we attach/detach uprobe to a file in tmpfs with huge=always.
Does this answer your question?
Thanks, Song
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