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[142.167.56.70]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7d09a0e2fc3sm1042617785a.19.2025.06.04.06.11.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Jun 2025 06:11:58 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1uMnuQ-000000004kJ-0VP6; Wed, 04 Jun 2025 10:11:58 -0300 Date: Wed, 4 Jun 2025 10:11:58 -0300 From: Jason Gunthorpe To: David Hildenbrand Cc: Hyesoo Yu , janghyuck.kim@samsung.com, zhaoyang.huang@unisoc.com, jaewon31.kim@gmail.com, Andrew Morton , John Hubbard , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: gup: fail migration when no migratable page to prevent CMA pinning Message-ID: <20250604131158.GA17991@ziepe.ca> References: <20250604095049.4052078-1-hyesoo.yu@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 72FEBA000B X-Stat-Signature: dw1pobbr1k7nx798dicbfgi8c5zqty5c X-Rspam-User: X-HE-Tag: 1749042720-881440 X-HE-Meta: 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 dItyLGKQ cl7VYouTRefBa4gN2XlC26J0dw4/JuU4Pe8kkJKgBTApyY7Lo6+4toUU1In5UDj54EfwpEMeM7ps/+Isv5MCbO7e0WR2YSNdXnkAnPvFKvEp1cntZAx2ESeOZnE+evplQMARJWEiw/Ka+cREtKv4EtthFGh9zZT3CE9KJOwvWZ+6JRa5bHVsrFrUMcKWdWkS+6m86KSKWExdrb6R8MDfa+a7FlY/EZSCYMFnFBLKVrUHEd8Lux9BrOmw6OIKd+tAER31EvDjIy4rS6mVWu9xYFSRoTuYhC3IXwoWlZiInawyKzbUMIK4cH4Is8JAHKb9WEH0iCp0w4P+Czu5RwKmdJ/sZPmwiiCM2KzkKQ8MJ7BuAz+vwDtdAAJ8BXgVbYyiepTwHLuFV3begYNb+OnJA2fH2Tw== 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 Wed, Jun 04, 2025 at 12:07:21PM +0200, David Hildenbrand wrote: > > Instead of retrying, this patch explicitly fails the migration attempt > > (-EBUSY) if no movable pages are found and unpinnable pages remain. > > This avoids infinite loops and gives user a clear signal to retry, > > rather then spinning inside kernel. > > Hmmm, that means we will return EBUSY to the caller. Are all users actually > prepared to deal with that? I don't think anyone is really prepared to deal with GUP temporarily failing.. Kernel is expected to sort it out. We tolerated the existing temporary failure due to its rarity and lack of a solution only. Either it can be gup'd or not. There should be no retry. Jason