Messages in this thread | | | Subject | Re: [PATCH] mm/damon: Validate if the pmd entry is present before accessing | From | Muchun Song <> | Date | Thu, 18 Aug 2022 13:12:16 +0800 |
| |
> On Aug 18, 2022, at 13:07, Baolin Wang <baolin.wang@linux.alibaba.com> wrote: > > > > 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.
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
| |