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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-719cb9aebddsm7110287b3.91.2025.07.24.21.47.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Jul 2025 21:48:00 -0700 (PDT) Date: Thu, 24 Jul 2025 21:47:48 -0700 (PDT) From: Hugh Dickins To: Baolin Wang cc: David Hildenbrand , Hugh Dickins , Patryk Kowalczyk , da.gomez@samsung.com, baohua@kernel.org, wangkefeng.wang@huawei.com, ioworker0@gmail.com, willy@infradead.org, ryan.roberts@arm.com, akpm@linux-foundation.org, eero.t.tamminen@intel.com, =?UTF-8?Q?Ville_Syrj=C3=A4l=C3=A4?= , "linux-mm@kvack.org" Subject: Re: regression - mm: shmem: add large folio support for tmpfs affect GPU performance. In-Reply-To: Message-ID: References: <63b69425-2fd1-2c77-06d6-e7ea25c92f34@google.com> <3f204974-26c8-4d5f-b7ae-4052cbfdf4ac@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: A6BB4180007 X-Stat-Signature: 6g17s7ghgnrip4uxj9gebenp5s84hkq1 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1753418882-458432 X-HE-Meta: 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 dm6nGZW1 DlP9X966sgyhYdVFhtrgTkJCN+kfufHbfstvKJRbcRvPRetzICii+C8TWDgAlrfOUXt4H4dFX7X+wnwfAjlrNZLFOZGCo0AWwdD8y8AwTbpIoFIwX5rEvldPQ4NaIDdS8qVHaHcN6oEbPssXfnKzGc3UcESGMZrXgJnmJDWosXJiBb478waWDxeULmwnqAMI4wAp/nqujdlQAM13ORsjx0iE5Y1pIrzX8X6n5onNoGLxcdDr3jbyY8IWBp+padGWFKWasnkKzOAPm+Ay32TuH6ONSy4Qzfryjal9PvKf6sN8WfYelXh5xsmfnYrI28QrPPv7fc+QOJRfYJ/H/MPAoo6bo9vGmrDJ/zRn54/S8HJdWJj31IXQFrEB7e0vJGqv9TUM/mKQNrA/4g4iCpPWYOGgwkg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 25 Jul 2025, Baolin Wang wrote: > > > > I hope to correct the logic of i915 driver's shmem allocation, by extending > > the shmem write length in the i915 driver to allocate PMD- sized THPs. IIUC, > > some sample fix code is as follows (untested). Patryk, could you help test > > it to see if this resolves your issue? Thanks. This patch cannot be the right fix. It may be a very sensible workaround for some in-kernel drivers (I've not looked or tried); but unless I misunderstand, it does nothing to restore userspace behaviour on a huge=always tmpfs. Please reread my comment earlier in the thread, in particular, Passing a new SIGBUS xfstest does not excuse a regression: strict PAGE_SIZE SIGBUS behaviour is fine for the newly-featured mTHPs or large folios, but not for the long-established huge=always. Thanks, Hugh