Hi:
On 2021/2/5 5:32, Mike Kravetz wrote:
> On 2/4/21 3:15 AM, Miaohe Lin wrote:
>> Shared mappings are allowed to be created without reservations since
>> commit c37f9fb11c97 ("hugetlb: allow huge page mappings to be created
>> without reservations"). Remove this obsolete comment which may cause
>> confusing.
>>
>> Signed-off-by: Miaohe Lin <[email protected]>
>> ---
>> mm/hugetlb.c | 1 -
>> 1 file changed, 1 deletion(-)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 9501ec6ad517..cf82629319ed 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -998,7 +998,6 @@ static bool vma_has_reserves(struct vm_area_struct *vma,
>> long chg)
>> return false;
>> }
>>
>> - /* Shared mappings always use reserves */
>
> I would not say the comment is entirely obsolete or does not apply here.
>
> As mentioned in the commit message, commit c37f9fb11c97 allowed hugetlb
> mappings to be created without reserves. It does this by supporting the
> MAP_NORESERVE flag which corresponds to the VM_NORESERVE vma flag.
>
> Right before this comment, a check is made for VM_NORESERVE and the
> routine will return. Therefore, by the time we get to this comment
> we know MAP_NORESERVE does not apply and there are reserves associated
> the shared mapping. In this case the comment is making a distinction
> between shared mappings which will always have reserves, and private
> mappings which may or may not have reserves depending on ownership.
>
Yes. If I think about it this way, the comment is really making a distinction
between shared mappings and private mappings when not in VM_NORESERVE case.
> I would suggest either leaving the comment as is, or modifying to include
I'd like to leave the comment as is. Many thanks for detailed explanation.
> the information above. To me, the three distinct blocks of code handling
> the NORESERVE, shared and private cases makes things fairly clear and
> the comment does apply in that context.
>
Many thanks again. :)
