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Tue, 3 Mar 2026 16:32:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772555573; bh=2Sl7aDOLhWSrJiQTk8Mgcff8zbQx95VCCn1PoV2FpZY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=nDNY2kBmYN+NuwFo3thQ/sWHyhRgfQeHTyWHfBniHNjPL0oQI7rwVP4BAGGka2BVO X2eonOQTORKw4QyAvBe8SHzxKvYYXyRcQkhx11QEY4iezHoyT64BtvBlX/zrslkt8o TmzoL3Y7w1lww4tC8ombT9QBKmAzjT4qFDkONDvfp2oR2t+yNFM1oHn2WfDjnZrf73 BuRfV7dQttvocIgye8lvZLJHANLxlbrfIiIalPMQ6tZuJeSyCAHEsrZwI4tw/4bZbD QmvrR7XLBlf8skl2ht4g6ytJIQCVDZVIfR9GCQISCD5amk7k+O3aibTOEoIWlXUS4c s5pzS6NssRWLA== Message-ID: Date: Tue, 3 Mar 2026 17:32:43 +0100 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 01/13] mm/migrate_device: Introduce migrate_pfn_from_page() helper To: Jordan Niethe , linux-mm@kvack.org Cc: balbirs@nvidia.com, matthew.brost@intel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, ziy@nvidia.com, apopple@nvidia.com, lorenzo.stoakes@oracle.com, lyude@redhat.com, dakr@kernel.org, airlied@gmail.com, simona@ffwll.ch, rcampbell@nvidia.com, mpenttil@redhat.com, jgg@nvidia.com, willy@infradead.org, linuxppc-dev@lists.ozlabs.org, intel-xe@lists.freedesktop.org, jgg@ziepe.ca, Felix.Kuehling@amd.com, jhubbard@nvidia.com, maddy@linux.ibm.com, mpe@ellerman.id.au, ying.huang@linux.alibaba.com References: <20260202113642.59295-1-jniethe@nvidia.com> <20260202113642.59295-2-jniethe@nvidia.com> <9ee22635-a219-47bb-a397-bc4e141b408d@kernel.org> <5182bb7d-f7cf-4b8e-8320-996c52fe24d8@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 3/3/26 06:52, Jordan Niethe wrote: > Hi > > On 2/3/26 20:22, David Hildenbrand (Arm) wrote: >> On 3/2/26 00:38, Jordan Niethe wrote: >>> Hi, >>> >> >> I'll go through he remainder of the patchset this week. > > Much appreciated. > >> >> While skimming over patch #2, I was wondering whether >> "page_to_migration_pfn()" would better fit "migration_pfn_to_page". > > I guess you were thinking about migration_pfn_/from/_page() rather than > "migration_pfn_to_page()"? Renaming it to page_to_migration_pfn() would > be fine. Yes. :) page_to_migration_pfn() and migration_pfn_to_page() But really, we should only be dealing with folio migration longterm ... > >> >> ... and I was wondering why that code deals with pages instead of folios. > >> >> E.g., >> >>     page = folio_page(folio, 0); >>     mpfn[i] = migrate_pfn_from_page(page); >> >> Should just be >> >>     mpfn[i] = folio_to_migration_pfn(folio); >> >> Right? > > This patch is quite limited, essentially just converts usages of > migrate_pfn(page_to_pfn()) to migration_pfn_from_page().  However, I > agree, there could be scope for moving some of those usages to folios. > > Was that example from drm_pagemap_migrate_populate_ram_pfn()?  There > 'page' goes on to be used elsewhere in the function so we'd need some > further refactoring to fully benefit. > > I see migrate_vma_collect_huge_pmd() as a candidate for a > folio_to_migration_pfn() function too. All that code should be converted to folios (unless I am missing something important). We only support migration of folios, and all ZONE_DEVICE pages correspond to folios. E.g., in migrate_vma_setup() we're implicitly converting from page to folio multiple times, which is rather wasteful. Now, I don't think the conversion is your responsibility :) But you'd provide the folio helpers and use them where we can already. I'm fine with leaving the code the still operates purely on page to be converted later. -- Cheers, David