Re: [PATCH 1/2] mm: shmem: avoid allocating huge pages larger than MAX_PAGECACHE_ORDER for shmem

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 2024/7/31 17:59, Kefeng Wang wrote:
> 
> 
> On 2024/7/31 16:56, Baolin Wang wrote:
>>
>>
>> On 2024/7/31 14:18, Barry Song wrote:
>>> On Wed, Jul 31, 2024 at 1:46 PM Baolin Wang
>>> <baolin.wang@linux.alibaba.com> wrote:
>>>>
>>>> Similar to commit d659b715e94ac ("mm/huge_memory: avoid PMD-size 
>>>> page cache
>>>> if needed"), ARM64 can support 512MB PMD-sized THP when the base 
>>>> page size is
>>>> 64KB, which is larger than the maximum supported page cache size 
>>>> MAX_PAGECACHE_ORDER.
>>>> This is not expected. To fix this issue, use 
>>>> THP_ORDERS_ALL_FILE_DEFAULT for
>>>> shmem to filter allowable huge orders.
>>>>
>>>> Fixes: e7a2ab7b3bb5 ("mm: shmem: add mTHP support for anonymous shmem")
>>>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>>>
>>> Reviewed-by: Barry Song <baohua@kernel.org>
>>
>> Thanks for reviewing.
>>
>>>
>>>> ---
>>>>   mm/shmem.c | 4 ++--
>>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/mm/shmem.c b/mm/shmem.c
>>>> index 2faa9daaf54b..a4332a97558c 100644
>>>> --- a/mm/shmem.c
>>>> +++ b/mm/shmem.c
>>>> @@ -1630,10 +1630,10 @@ unsigned long 
>>>> shmem_allowable_huge_orders(struct inode *inode,
>>>>          unsigned long within_size_orders = 
>>>> READ_ONCE(huge_shmem_orders_within_size);
>>>>          unsigned long vm_flags = vma->vm_flags;
>>>>          /*
>>>> -        * Check all the (large) orders below HPAGE_PMD_ORDER + 1 that
>>>> +        * Check all the (large) orders below MAX_PAGECACHE_ORDER + 
>>>> 1 that
>>>>           * are enabled for this vma.
>>>
>>> Nit:
>>> THP_ORDERS_ALL_FILE_DEFAULT should be self-explanatory enough.
>>> I feel we don't need this comment?
>>
>> Sure.
>>
>> Andrew, please help to squash the following changes into this patch. 
>> Thanks.
> 
> Maybe drop unsigned long orders too?
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 6af95f595d6f..8485eb6f2ec4 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1638,11 +1638,6 @@ unsigned long shmem_allowable_huge_orders(struct 
> inode *inode,
>          unsigned long mask = READ_ONCE(huge_shmem_orders_always);
>          unsigned long within_size_orders = 
> READ_ONCE(huge_shmem_orders_within_size);
>          unsigned long vm_flags = vma ? vma->vm_flags : 0;
> -       /*
> -        * Check all the (large) orders below HPAGE_PMD_ORDER + 1 that
> -        * are enabled for this vma.
> -        */
> -       unsigned long orders = BIT(PMD_ORDER + 1) - 1;
>          bool global_huge;
>          loff_t i_size;
>          int order;
> @@ -1698,7 +1693,7 @@ unsigned long shmem_allowable_huge_orders(struct 
> inode *inode,
>          if (global_huge)
>                  mask |= READ_ONCE(huge_shmem_orders_inherit);
> 
> -       return orders & mask;
> +       return THP_ORDERS_ALL_FILE_DEFAULT & mask;
>   }

Yes. Good point. Thanks.
(Hope Andrew can help to squash these changes :))