> On Aug 1, 2019, at 7:50 AM, Oleg Nesterov <oleg@xxxxxxxxxx> 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
