Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 18 Aug 2022 13:07:13 +0800 | Subject | Re: [PATCH] mm/damon: Validate if the pmd entry is present before accessing | From | Baolin Wang <> |
| |
On 8/18/2022 11:39 AM, Muchun Song wrote: > > >> On Aug 18, 2022, at 10:57, Baolin Wang <baolin.wang@linux.alibaba.com> wrote: >> >> >> >> 在 8/18/2022 10:41 AM, Muchun Song 写道: >>>> On Aug 17, 2022, at 14:21, Baolin Wang <baolin.wang@linux.alibaba.com> 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@linux.alibaba.com> >>>> --- >>>> 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.
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.
>> >>> 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
| ![\](/images/icornerr.gif) |