> On Aug 18, 2022, at 13:07, Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
>
>
>
> On 8/18/2022 11:39 AM, Muchun Song wrote:
>>> On Aug 18, 2022, at 10:57, Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
>>>
>>>
>>>
>>> 在 8/18/2022 10:41 AM, Muchun Song 写道:
>>>>> On Aug 17, 2022, at 14:21, Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
>>>>>
>>>>> The pmd_huge() is used to validate if the pmd entry is mapped by a huge
>>>>> page, also including the case of non-present (migration or hwpoisoned)
>>>>> pmd entry on arm64 or x86 architectures. Thus we should validate if it
>>>>> is present before making the pmd entry old or getting young state,
>>>>> otherwise we can not get the correct corresponding page.
>>>>>
>>>>> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>>>>> ---
>>>>> mm/damon/vaddr.c | 10 ++++++++++
>>>>> 1 file changed, 10 insertions(+)
>>>>>
>>>>> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
>>>>> index 3c7b9d6..1d16c6c 100644
>>>>> --- a/mm/damon/vaddr.c
>>>>> +++ b/mm/damon/vaddr.c
>>>>> @@ -304,6 +304,11 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
>>>>>
>>>>> if (pmd_huge(*pmd)) {
>>>>> ptl = pmd_lock(walk->mm, pmd);
>>>>> + if (!pmd_present(*pmd)) {
>>>> Unluckily, we should use pte_present here. See commit c9d398fa23788. We can use
>>>> huge_ptep_get() to get a hugetlb pte, so it’s better to put the check after
>>>> pmd_huge.
>>>
>>> IMO this is not the case for hugetlb, and the hugetlb case will be handled by damon_mkold_hugetlb_entry(), which already used pte_present() for hugetlb case.
>> Well, I thought it is hugetlb related since I saw the usage of pmd_huge. If it is THP case, why
>> not use pmd_trans_huge?
>
> IIUC, it can not guarantee the pmd is present if pmd_trans_huge() returns true on all architectures, at least on X86, we still need pmd_present() validation. So changing to pmd_trans_huge() does not make code simpler from my side, and I prefer to keep this patch.
I am not suggesting you change it to pmd_trans_huge() in this patch, I am just expressing
my curious. At least, it is a little confusing to me.
>
> Maybe we can send another cleanup patch to replace pmd_huge() with pmd_trans_huge() for THP case to make code more readable? How do you think? Thanks.
Yep, make sense to me.
Thanks.
>
>>>
>>>> Cc Mike to make sure I am not missing something.
>>>> Muchun,
>>>> Thanks.
>>>>> + spin_unlock(ptl);
>>>>> + return 0;
>>>>> + }
>>>>> +
>>>>> if (pmd_huge(*pmd)) {
>>>>> damon_pmdp_mkold(pmd, walk->mm, addr);
>>>>> spin_unlock(ptl);
>>>>> @@ -431,6 +436,11 @@ static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
>>>>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>>>> if (pmd_huge(*pmd)) {
>>>>> ptl = pmd_lock(walk->mm, pmd);
>>>>> + if (!pmd_present(*pmd)) {
>>>>> + spin_unlock(ptl);
>>>>> + return 0;
>>>>> + }
>>>>> +
>>>>> if (!pmd_huge(*pmd)) {
>>>>> spin_unlock(ptl);
>>>>> goto regular_page;
>>>>> --
>>>>> 1.8.3.1
