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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id z133sm10523570qka.20.2020.11.23.09.15.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Nov 2020 09:15:03 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1khFQc-00A6rX-Ou; Mon, 23 Nov 2020 13:15:02 -0400 Date: Mon, 23 Nov 2020 13:15:02 -0400 From: Jason Gunthorpe To: Pavel Tatashin Cc: Michal Hocko , linux-mm , Andrew Morton , Vlastimil Babka , LKML , David Hildenbrand , Oscar Salvador , Dan Williams , Sasha Levin , Tyler Hicks , Joonsoo Kim , sthemmin@microsoft.com Subject: Re: Pinning ZONE_MOVABLE pages Message-ID: <20201123171502.GX244516@ziepe.ca> References: <20201123090129.GD27488@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: On Mon, Nov 23, 2020 at 11:06:21AM -0500, Pavel Tatashin wrote: > What I mean here is allowing users to guarantee that the page's PA is > going to stay the same. Sort of a stronger mlock. Mlock only > guarantees that the page is not swapped, but something like You've just described get/pin_user_pages(), that is exactly what it is for. I agree with the other emails, ZONE_MOVABLE needs to be reconciled with FOLL_LONGTERM - most likely by preventing ZONE_MOVABLE pages from being returned. This will need migration like CMA does and the point about faulting is only an optimization to prevent fault then immediate migration. Jason