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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rb7U1-00000005uni-0Zym; Fri, 16 Feb 2024 23:19:05 +0000 Date: Fri, 16 Feb 2024 23:19:05 +0000 From: Matthew Wilcox To: Sidhartha Kumar Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, apopple@nvidia.com Subject: Re: [PATCH v2 4/6] mm/migrate_device: convert __migrate_device_pages() to folios Message-ID: References: <20240216211320.222431-1-sidhartha.kumar@oracle.com> <20240216211320.222431-4-sidhartha.kumar@oracle.com> <71db0ad0-a385-8572-7bea-bb11f76a6345@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <71db0ad0-a385-8572-7bea-bb11f76a6345@oracle.com> X-Rspamd-Queue-Id: 7D688C0012 X-Rspam-User: X-Stat-Signature: 1zgnqkpqu6xcyxu5uta93pahwkx3titc X-Rspamd-Server: rspam01 X-HE-Tag: 1708125550-318268 X-HE-Meta: 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 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 Fri, Feb 16, 2024 at 02:00:31PM -0800, Sidhartha Kumar wrote: > On 2/16/24 1:55 PM, Matthew Wilcox wrote: > > On Fri, Feb 16, 2024 at 01:13:18PM -0800, Sidhartha Kumar wrote: > > > Use migrate_pfn_to_folio() so we can work with folios directly in > > > __migrate_device_pages(). > > > > i don't understand why this would be correct if we have multipage > > folios. > > > > Alistair mentioned that he is working on order > 0 device page support so I > was under the impression that currently device pages are only order 0. That might well be true, but I'm *very* uncomfortable with doing a folio conversion in core MM that won't work with large folios. We need to consider what will happen with large device folios. (for filesystems, I am less bothered. Individual filesystems control whether they see large folios or not, and for lesser filesystems it may never be worth converting them to support large folios)