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[2003:cb:c707:3900:757e:83f8:a99d:41ae]) by smtp.gmail.com with ESMTPSA id q17-20020adfea11000000b0030639a86f9dsm3578463wrm.51.2023.05.17.11.23.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 May 2023 11:23:34 -0700 (PDT) Message-ID: Date: Wed, 17 May 2023 20:23:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH] tee: add FOLL_LONGTERM for CMA case when alloc shm Content-Language: en-US To: Sumit Garg , Christoph Hellwig , Xiaoming Ding Cc: Jens Wiklander , Matthias Brugger , AngeloGioacchino Del Regno , op-tee@lists.trustedfirmware.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, fei.xu@mediatek.com, srv_heupstream@mediatek.com, linux-mm@kvack.org References: <20230517031856.19660-1-xiaoming.ding@mediatek.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17.05.23 12:19, Sumit Garg wrote: > On Wed, 17 May 2023 at 15:06, Christoph Hellwig wrote: >> >> On Wed, May 17, 2023 at 02:56:13PM +0530, Sumit Garg wrote: >>> Do you mean a pinned user-space page can be paged out automatically? >> >> No, pinned pages can't be paged out. >> >> But a short term pin implies it will be release after a short delay, >> and it is feasible for wait for the pin to go away. > > Okay, I see. I would be interested to know the ranges for that short > delay. I guess it may depend on how much memory pressure there is... > In general: if user space controls it -> possibly forever -> long-term. Even if in most cases it's a short delay: there is no trusting on user space. For example, iouring fixed buffers keep pages pinned until user space decides to unregistered the buffers -> long-term. Short-term is, for example, something like O_DIRECT where we pin -> DMA -> unpin in essentially one operation. -- Thanks, David / dhildenb