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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8cd6f4878bbsm718502285a.4.2026.03.09.10.54.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Mar 2026 10:54:23 -0700 (PDT) Date: Mon, 9 Mar 2026 13:54:20 -0400 From: Gregory Price To: Shivank Garg Cc: akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@kernel.org, willy@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, dave@stgolabs.net, Jonathan.Cameron@huawei.com, rkodsara@amd.com, vkoul@kernel.org, bharata@amd.com, sj@kernel.org, weixugc@google.com, dan.j.williams@intel.com, rientjes@google.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, dave.hansen@intel.com, hannes@cmpxchg.org, jhubbard@nvidia.com, peterx@redhat.com, riel@surriel.com, shakeel.butt@linux.dev, stalexan@redhat.com, tj@kernel.org, nifan.cxl@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mike Day Subject: Re: [RFC PATCH v4 4/6] mm/migrate: add copy offload registration infrastructure Message-ID: References: <20260309120725.308854-3-shivankg@amd.com> <20260309120725.308854-12-shivankg@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260309120725.308854-12-shivankg@amd.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: B686DC000B X-Stat-Signature: g38c9qt1kf6chyb1dwznes7cab776ffp X-Rspam-User: X-HE-Tag: 1773078864-988576 X-HE-Meta: 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 0D8rx8Fu gMettfTB7+G/u0oHIjlpXP47aNlr2F2VvSMjJlFNXLpqeuPPvV+vVWJ4Oq+rk7xmu0XCUP/dFvonn+NCOjxD/PyOQd3ULDJrgzzQlz5P9ULG3CJ+pqMVpcKreeqAt9vNUJxl1zioCohNNXFcpPiXvgzIWi7w8w58MCzMvd4wOmfaM3Gp0Yajv5Kp7khvzlQJ/wxifdDGnHTUiRGz+v7rTWpbH656UThO+sAvkzCoLfZIcxudqh59KHiqYv+yYHFLooeYc8UO4emvNdl059ymfm+L668kU9yRteFPa+81zZBPmgbQTKd6wuYK4a56qSg+y45CvW6pWAvwZl1Q2+qV/DNE5rlha7HUyE2H/vhzlRRKPaIpVLQGIgibAfrXdw63QguetbU3RbVSkx4hD/nNhahZjQA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 09, 2026 at 12:07:29PM +0000, Shivank Garg wrote: ... snip ... > > Only one migrator can be active a time. A second registration returns > -EBUSY, and only the active migrator can stop itself. The static_call > dispatch is under SRCU so synchronize_srcu() in stop path guarantees > no in-flight copy before the module reference is dropped. > ... snip ... > @@ -1820,11 +1833,18 @@ static int migrate_pages_batch(struct list_head *from, > > +#ifdef CONFIG_MIGRATION_COPY_OFFLOAD > + /* Check if the offload driver wants to batch for this reason */ > + if (static_branch_unlikely(&migrate_offload_enabled)) > + do_batch = static_call(migrate_should_batch)(reason); > +#endif > + should the migrate_should_batch call also be done under srcu? In theory it's an incredibly small window, but there is a race window. ~Gregory