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[85.23.51.1]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a8a95661aasm3290978e87.68.2026.05.12.05.08.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 May 2026 05:08:21 -0700 (PDT) Message-ID: <7e3abb7c-c57d-419a-969a-fcd150ccca99@redhat.com> Date: Tue, 12 May 2026 15:08:20 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 2/5] mm: Add helper to convert HMM pfn to migrate pfn To: "David Hildenbrand (Arm)" , linux-mm@kvack.org Cc: dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-kernel@vger.kernel.org, Jason Gunthorpe , Leon Romanovsky , Alistair Popple , Balbir Singh , Zi Yan , Matthew Brost , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko References: <20260505184421.2324798-1-mpenttil@redhat.com> <20260505184421.2324798-3-mpenttil@redhat.com> <4a9c4170-c6b7-424c-969c-19240f07e46b@kernel.org> Content-Language: en-US From: =?UTF-8?Q?Mika_Penttil=C3=A4?= In-Reply-To: <4a9c4170-c6b7-424c-969c-19240f07e46b@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/12/26 14:43, David Hildenbrand (Arm) wrote: >> + >> +/** >> + * migrate_hmm_range_setup() - prepare to migrate a range of memory >> + * @range: contains pointer to struct migrate_vma to be set up. >> + * >> + * When collecting has been done with hmm_range_fault(), this >> + * should be called next, and completes range->migrate by >> + * populating migrate->src[] and migrate->dst[] >> + * using range->hmm_pfns[]. >> + * Also, migrate->cpages and migrate->npages get initialized. >> + * After migrate_hmm_range_setup(), range->migrate is good >> + * for the rest of the migrate_vma_* flow. >> + */ >> +void migrate_hmm_range_setup(struct hmm_range *range) >> +{ >> + struct migrate_vma *migrate = range->migrate; >> + >> + if (!migrate) >> + return; >> + >> + migrate->npages = (migrate->end - migrate->start) >> PAGE_SHIFT; >> + migrate->cpages = 0; >> + >> + for (unsigned long i = 0; i < migrate->npages; i++) { >> + unsigned long pfn = range->hmm_pfns[i]; >> + >> + /* >> + * We are only interested in entries to be >> + * migrated. >> + */ >> + if (!(pfn & HMM_PFN_MIGRATE)) { >> + migrate->src[i] = 0; >> + migrate->dst[i] = 0; >> + continue; >> + } >> + >> + migrate->cpages++; >> + >> + /* HMM_PFN_MIGRATE without HMM_PFN_VALID denotes the special zero page */ >> + if (pfn & (HMM_PFN_VALID)) > No need for () ack > >> + migrate->src[i] = migrate_pfn(page_to_pfn(hmm_pfn_to_page(pfn))) > Is there no easier way to avoid going through a page? > > I guess you really just want "migrate_pfn(pfn & ~HMM_PFN_FLAGS)". > > Maybe add a hmm_pfn_to_pfn() helper that does the "pfn & ~HMM_PFN_FLAGS" ? Basically yes. I noticed this was helpful for instance with the "separate address space for device_private" patchset not to depend on the coding. > >> + | MIGRATE_PFN_MIGRATE; > We (MM folks) usually put the | onto the previous line to then properly indent > the second line Okay I will change. > > migrate->src[i] = migrate_pfn(page_to_pfn(hmm_pfn_to_page(pfn))) | > MIGRATE_PFN_MIGRATE; > >> + else >> + migrate->src[i] = MIGRATE_PFN_MIGRATE; > It might be cleaner to just set migrate->src[i] = 0; here and to unconditionally > > migrate->src[i] |= MIGRATE_PFN_MIGRATE; > > So you don't have the MIGRATE_PFN_MIGRATE on two paths. Good point. > >> + >> + migrate->src[i] |= (pfn & HMM_PFN_WRITE) ? MIGRATE_PFN_WRITE : 0; >> + migrate->src[i] |= (pfn & HMM_PFN_COMPOUND) ? MIGRATE_PFN_COMPOUND : 0; >> + migrate->dst[i] = 0; >> + } >> + >> + if (migrate->cpages) >> + migrate_vma_unmap(migrate); > Can you remind me why we do this here, in the setup() phase? The function doc > does not really describe that. It is to be in par what migrate_vma_setup() does today after the "collect" phase. Thanks, Mika >