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

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Message-ID: <72978e3a-ee67-47d4-b06d-e911bc5d57ff@redhat.com>
Date: Fri, 2 May 2025 09:18:41 +0200
From: David Hildenbrand <david@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Daniel Gomez <da.gomez@...nel.org>,
 Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, willy@...radead.org,
 wangkefeng.wang@...wei.com, 21cnbao@...il.com, ryan.roberts@....com,
 ioworker0@...il.com, da.gomez@...sung.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, regressions@...ts.linux.dev,
 intel-gfx@...ts.freedesktop.org, Eero Tamminen <eero.t.tamminen@...el.com>
Subject: Re: [REGRESSION] Re: [PATCH v3 3/6] mm: shmem: add large folio
 support for tmpfs

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