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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D4BD21C0011 X-Stat-Signature: yid57qkpxfhk4nidtuc6yxxcegqy4cxs X-Rspam-User: X-HE-Tag: 1738250979-252500 X-HE-Meta: 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 J+P4BGTa 7fu5XLqiT1HMj21qlji2eTJzM5AcKe04amOVLEqWKd9rbuB8cGSo1azX0nZDpkciyaM7qcHaDYaOj9qel4ZmP6KTj+pHRGW2lPVhLWH+UL6rpk35t098+iowxL8ao1hP21IB/Ksue7t/DLfJhBmWVGnYZXa8iYXYxCHOTq1r6gmFeWTzoC53+GLb0hE6/tyw7+7n6w7VRzmtVV1LU82KQo/AGNo1PGhZDdkdoI95anluNh72mVphwsyeEasEDHQlEx6JObncSrQOgwxT9MaNfbJzt8OcVYA8jYhdsRLiXF3ndD90X6LJR+bQwNc7IRauJGY1xZMHu86y+UCibOHx0fxh2Fh4JlsL/SY4oZqlSPhg149QeBpBgQsVfWer1gDUYjGr+9tJjvITBPlfZPdQExNgy0iILWKlTjEl6K5ZiXt60+9G+ulq2fZW+tSzTbsa6wxx2 X-Bogosity: Ham, tests=bogofilter, spamicity=0.003821, 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 30.01.25 14:31, Simona Vetter wrote: > On Thu, Jan 30, 2025 at 10:37:06AM +0100, David Hildenbrand wrote: >> On 30.01.25 01:27, Alistair Popple wrote: >>> On Wed, Jan 29, 2025 at 12:58:02PM +0100, David Hildenbrand wrote: >>>> Let's document how this function is to be used, and why the requirement >>>> for the folio lock might maybe be dropped in the future. >>> >>> Sorry, only just catching up on your other thread. The folio lock was to ensure >>> the GPU got a chance to make forward progress by mapping the page. Without it >>> the CPU could immediately invalidate the entry before the GPU had a chance to >>> retry the fault. >>>> Obviously performance wise having such thrashing is terrible, so should >>> really be avoided by userspace, but the lock at least allowed such programs >>> to complete. >> >> Thanks for the clarification. So it's relevant that the MMU notifier in >> remove_device_exclusive_entry() is sent after taking the folio lock. >> >> However, as soon as we drop the folio lock, remove_device_exclusive_entry() >> will become active, lock the folio and trigger the MMU notifier. >> >> So the time it is actually mapped into the device is rather I meant to say "rather short." :) > > Looks like you cut off a bit here (or mail transport did that somewhere), > but see my other reply I don't think this is a legit use-case. So we don't > have to worry. In that case, we would need the folio lock in the future. > Well beyond documenting that if userspace concurrently thrashes > the same page with both device atomics and cpu access it will stall real > bad. I'm curious, is locking between device-cpu or device-device something that can happen frequently? In that case, you would get that trashing naturally? -- Cheers, David / dhildenb