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[2003:cb:c713:d600:afc5:4312:176f:3fb0]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-441b2aecc20sm93468795e9.13.2025.05.02.08.31.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 02 May 2025 08:31:47 -0700 (PDT) Message-ID: Date: Fri, 2 May 2025 17:31:46 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [REGRESSION] Re: [PATCH v3 3/6] mm: shmem: add large folio support for tmpfs To: Daniel Gomez , Baolin Wang Cc: =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= , akpm@linux-foundation.org, hughd@google.com, willy@infradead.org, wangkefeng.wang@huawei.com, 21cnbao@gmail.com, ryan.roberts@arm.com, ioworker0@gmail.com, da.gomez@samsung.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, regressions@lists.linux.dev, intel-gfx@lists.freedesktop.org, Eero Tamminen References: <035bf55fbdebeff65f5cb2cdb9907b7d632c3228.1732779148.git.baolin.wang@linux.alibaba.com> <57dc4929-268b-4f3f-a0f8-43d6ec85974f@linux.alibaba.com> <72978e3a-ee67-47d4-b06d-e911bc5d57ff@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 02.05.25 15:10, Daniel Gomez wrote: > On Fri, May 02, 2025 at 09:18:41AM +0100, David Hildenbrand wrote: >> 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. > > Thanks for reminding me. I forgot we finally changed it. > > Could the performance drop be due to the driver no longer using PMD-level pages? I suspect that the faulting logic will now go to a smaller order first, indeed. ... trying to digest shmem_allowable_huge_orders() and shmem_huge_global_enabled(), having a hard time trying to isolate the tmpfs case: especially, if we run here into the vma vs. !vma case. Without a VMA, I think we should have "mpfs will allow getting a highest order hint based on and fallocate paths, then will try each allowable order". With a VMA (no access hint), "we still use PMD-sized order to locate huge pages due to lack of a write size hint." So if we get a fallocate()/write() that is, say, 1 MiB, we'd now allocate an 1 MiB folio instead of a 2 MiB one. -- Cheers, David / dhildenb