Re: [REGRESSION] Re: [PATCH v3 3/6] mm: shmem: add large folio support for tmpfs

[David Hildenbrand <david@redhat.com>]

On 02.05.25 03:02, Baolin Wang wrote:
> 
> 
> On 2025/4/30 21:24, Daniel Gomez wrote:
>> On Wed, Apr 30, 2025 at 02:20:02PM +0100, Ville Syrjälä wrote:
>>> On Wed, Apr 30, 2025 at 02:32:39PM +0800, Baolin Wang wrote:
>>>> On 2025/4/30 01:44, Ville Syrjälä wrote:
>>>>> On Thu, Nov 28, 2024 at 03:40:41PM +0800, Baolin Wang wrote:
>>>>> Hi,
>>>>>
>>>>> This causes a huge regression in Intel iGPU texturing performance.
>>>>
>>>> Unfortunately, I don't have such platform to test it.
>>>>
>>>>>
>>>>> I haven't had time to look at this in detail, but presumably the
>>>>> problem is that we're no longer getting huge pages from our
>>>>> private tmpfs mount (done in i915_gemfs_init()).
>>>>
>>>> IIUC, the i915 driver still limits the maximum write size to PAGE_SIZE
>>>> in the shmem_pwrite(),
>>>
>>> pwrite is just one random way to write to objects, and probably
>>> not something that's even used by current Mesa.
>>>
>>>> which prevents tmpfs from allocating large
>>>> folios. As mentioned in the comments below, tmpfs like other file
>>>> systems that support large folios, will allow getting a highest order
>>>> hint based on the size of the write and fallocate paths, and then will
>>>> attempt each allowable huge order.
>>>>
>>>> Therefore, I think the shmem_pwrite() function should be changed to
>>>> remove the limitation that the write size cannot exceed PAGE_SIZE.
>>
>> To enable mTHP on tmpfs, the necessary knobs must first be enabled in sysfs
>> as they are not enabled by default IIRC (only THP, PMD level). Ville, I
>> see i915_gemfs the huge=within_size mount option is passed. Can you confirm
>> if /sys/kernel/mm/transparent_hugepage/hugepages-*/enabled are also marked as
>> 'always' when the regression is found?
> 
> The tmpfs mount will not be controlled by
> '/sys/kernel/mm/transparent_hugepage/hugepages-*Kb/enabled' (except for
> the debugging options 'deny' and 'force').

Right, IIRC as requested by Willy, it should behave like other FSes 
where there is no control over the folio size to be used.

-- 
Cheers,

David / dhildenb