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[142.68.128.5]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4609784bfe1sm3525541cf.0.2024.10.16.08.45.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Oct 2024 08:45:55 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1t16Dj-000Cg0-BG; Wed, 16 Oct 2024 12:45:55 -0300 Date: Wed, 16 Oct 2024 12:45:55 -0300 From: Jason Gunthorpe To: Alistair Popple Cc: Yonatan Maman , nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, linux-mm@kvack.org, herbst@redhat.com, lyude@redhat.com, dakr@redhat.com, airlied@gmail.com, simona@ffwll.ch, leon@kernel.org, jglisse@redhat.com, akpm@linux-foundation.org, dri-devel@lists.freedesktop.org, bskeggs@nvidia.com, Gal Shalom Subject: Re: [PATCH v1 1/4] mm/hmm: HMM API for P2P DMA to device zone pages Message-ID: <20241016154555.GE4020792@ziepe.ca> References: <20241015152348.3055360-1-ymaman@nvidia.com> <20241015152348.3055360-2-ymaman@nvidia.com> <87frow8wdk.fsf@nvdebian.thelocal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87frow8wdk.fsf@nvdebian.thelocal> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BFF1514000B X-Stat-Signature: 11rn9exhun5fj3g5iw6s9r5h7zii1x87 X-HE-Tag: 1729093550-624600 X-HE-Meta: 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 vi5bQoWN zC2Cqj/2NtyAkx6D+qUn9fYGo+7NV7ggJIS2PI2Wg8ldap7AmuZSqXOVQY/r44syXb0x7m6u/BxKSmm+3kSsrD6QxkWxGQssNm3Zuw+Yi5lqXsXIL3k/9cF8NvhsMybqP8HG3RhjdW63OONRYoZdTjhHImrCneg6TBviKEDj/f7JrE4tnxZoNze8V/w6L+8g9EUPeA37USmMHG/mu46dzgxWb50MFoMaaaYelDhycsfj+4sjj9yN9095mWNDaOn6z65XD/xlzjav0/YkhVu2SK+HX8iHT3iVvDAKi X-Bogosity: Ham, tests=bogofilter, spamicity=0.000006, 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 Wed, Oct 16, 2024 at 04:10:53PM +1100, Alistair Popple wrote: > On that note how is the refcounting of the returned p2pdma page expected > to work? We don't want the driver calling hmm_range_fault() to be able > to pin the page with eg. get_page(), so the returned p2pdma page should > have a zero refcount to enforce that. I think that is just the rule for hmm stuff in general, don't touch the refcount. We don't need to enforce, it we don't know what else the driver will want to use that P2P page for after all. It might stick it in a VMA for some unrelated reason. Jason