On 1/3/21 11:10 PM, Li Xinhai wrote:
>
>
> On 1/4/21 11:55 AM, Mike Kravetz wrote:
>> I believe the only case where your patch produced incorrect results is
>> when the range was within a vma that was smaller than PUD_SIZE. Do you
>> agree?
>>
> Not exactly. We need to consider for vma which span at least one
> PUD_SIZE after align its vm_start and vm_end.
>
I know that I provided an incorrect example again. Sorry (again)!
Can you provide an example where adding the simple check for vma size less
than PUD_SIZE to your original patch will not work. The logic in your V2
patch is correct. However, I am having a hard time finding a problem with
this simpler approach.
--
Mike Kravetz
>> If that is the case, then how about just adding the following to your patch?
>> I think this is simpler and faster than the 'range_in_vma' checking I proposed.
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 49990c0a02a3..716d1e58a7ae 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -5261,7 +5261,9 @@ void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
>> {
>> unsigned long a_start, a_end;
>> - if (!(vma->vm_flags & VM_MAYSHARE))
>> + /* Quick check for vma capable of pmd sharing */
>> + if (!(vma->vm_flags & VM_MAYSHARE) ||
>> + (vma->vm_start - vma->vm_end) < PUD_SIZE)
>> return;
>> /* Extend the range to be PUD aligned for a worst case scenario */
>
> Your suggestion is good, we are able to simplify the code a bit, with
> less comparison, and maybe easier to follow. I will send a new patch to
> review.
