On 2022/3/3 2:43, Yang Shi wrote:
> On Tue, Mar 1, 2022 at 1:07 AM Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
>>
>> On 2022/3/1 7:57, Yang Shi wrote:
>>> The hugepage_vma_check() called by khugepaged_enter_vma_merge() does
>>> check VM_NO_KHUGEPAGED. Remove the check from caller and move the check
>>> in hugepage_vma_check() up.
>>>
>>> More checks may be run for VM_NO_KHUGEPAGED vmas, but MADV_HUGEPAGE is
>>> definitely not a hot path, so cleaner code does outweigh.
>>>
>>> Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
>>> ---
>>> mm/khugepaged.c | 9 ++++++---
>>> 1 file changed, 6 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>>> index 131492fd1148..82c71c6da9ce 100644
>>> --- a/mm/khugepaged.c
>>> +++ b/mm/khugepaged.c
>>> @@ -366,8 +366,7 @@ int hugepage_madvise(struct vm_area_struct *vma,
>>> * register it here without waiting a page fault that
>>> * may not happen any time soon.
>>> */
>>> - if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
>>> - khugepaged_enter_vma_merge(vma, *vm_flags))
>>> + if (khugepaged_enter_vma_merge(vma, *vm_flags))
>>> return -ENOMEM;
>>> break;
>>> case MADV_NOHUGEPAGE:
>>> @@ -446,6 +445,9 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
>>> if (!transhuge_vma_enabled(vma, vm_flags))
>>> return false;
>>>
>>> + if (vm_flags & VM_NO_KHUGEPAGED)
>>> + return false;
>>> +
>>
>> This patch does improve the readability. But I have a question.
>> It seems VM_NO_KHUGEPAGED is not checked in the below if-condition:
>>
>> /* Only regular file is valid */
>> if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
>> (vm_flags & VM_EXEC)) {
>> struct inode *inode = vma->vm_file->f_inode;
>>
>> return !inode_is_open_for_write(inode) &&
>> S_ISREG(inode->i_mode);
>> }
>>
>> If we return false due to VM_NO_KHUGEPAGED here, it seems it will affect the
>> return value of this CONFIG_READ_ONLY_THP_FOR_FS condition check.
>> Or am I miss something?
>
> Yes, it will return false instead of true if that file THP check is
> true, but wasn't that old behavior actually problematic? Khugepaged
> definitely can't collapse VM_NO_KHUGEPAGED vmas even though it
> satisfies all the readonly file THP checks. With the old behavior
> khugepaged may scan an exec file hugetlb vma IIUC although it will
> fail later due to other page sanity checks, i.e. page compound check.
Sounds reasonable to me. Khugepaged shouldn't collapse VM_NO_KHUGEPAGED vmas.
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Thanks.
>
>>
>> Thanks.
>>
>>> if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
>>> vma->vm_pgoff, HPAGE_PMD_NR))
>>> return false;
>>> @@ -471,7 +473,8 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
>>> return false;
>>> if (vma_is_temporary_stack(vma))
>>> return false;
>>> - return !(vm_flags & VM_NO_KHUGEPAGED);
>>> +
>>> + return true;
>>> }
>>>
>>> int __khugepaged_enter(struct mm_struct *mm)
>>>
>>
>>
> .
>
