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b=Hmcc79SCMgkni+sJcI/8+5HS+mWVebR4K17jduHY+OeIRwe3RK2DsWPisDmo7IwUP ioOp2IvwyIMA9FPmBE5YoQhvULFL7z5bpL4wPfIDMrrs0DVAvrfZCHn+xzYouW6v8U OnQgP13ik5xmMRTLDqGyp7T76KG1QI+w7o3ZAsg54n1pHo8ihKtwCfUq5N6WiYvEZ3 Eq3dFy2qF9ysM3jnm5Dzgg8096y06bJzaODWjkYoIebQgh2D7kpKk1cnHpdUcUN2D1 J5L2VQvvvLeMURZ7t9ugzOi4gr+Hrl54Ri8knQSZE9RvKaFQFY5/T+jqMz3bvk/vBV Q/MaQyh+3bOKg== Message-ID: Date: Tue, 9 Jun 2026 14:55:00 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/7] mm/migrate: skip data copy for already-copied folios To: "Garg, Shivank" , Zi Yan Cc: akpm@linux-foundation.org, kinseyho@google.com, weixugc@google.com, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, willy@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, dave@stgolabs.net, rkodsara@amd.com, vkoul@kernel.org, bharata@amd.com, sj@kernel.org, rientjes@google.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, dave.hansen@intel.com, hannes@cmpxchg.org, jhubbard@nvidia.com, peterx@redhat.com, riel@surriel.com, shakeel.butt@linux.dev, stalexan@redhat.com, tj@kernel.org, nifan.cxl@gmail.com, jic23@kernel.org, aneesh.kumar@kernel.org, nathan.lynch@amd.com, Frank.li@nxp.com, djbw@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260428155043.39251-2-shivankg@amd.com> <20260428155043.39251-8-shivankg@amd.com> <810e9a58-9c08-4f5e-af5f-866685ca09b2@kernel.org> <7e6a7626-5a1b-4672-91bd-85b0f4ee2ecb@amd.com> <7430d69a-616b-40cf-a2e8-6ef4e57b6857@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: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: E664B40011 X-Stat-Signature: g57zofy6dzbkj98ea5mucgizwe5tg83w X-Rspam-User: X-HE-Tag: 1781009713-124185 X-HE-Meta: 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 ltaMSImb m9mXBK3yrd0llmIse8Cciahxnxjxs7gF5BBOGIjmKuAW/lHHY+469c7AaVQn9dDVQu9K6NSP93vrpcehajYkTaMRNr+QnOuxjwSjmAj7g/isA831mgGyakXrPSWmeRjMtAyWeczVQU6apd/FrRSHnr4qcAwW3o76w53/HzSX3c4vEIjA+mXLrlI5CruVnDQxBFncF/BlyQaNbptuhz88oQke9z53mPoU/kJSeDlyqRGtcpJbUr1lu/1Fdd3OWj0w/cwxZN0AqiIYsaD46zfJjS/phdNSOcJU9TvSaq+pY6fGoYBHYTqdeTgKDsQEK0Jh0QpuuA7A3infCXX+mGujojoKqUA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/8/26 21:32, Garg, Shivank wrote: > > > On 6/8/2026 9:13 PM, David Hildenbrand (Arm) wrote: >> On 6/8/26 17:41, Zi Yan wrote: >>> >>> >>> IIRC, multithreaded copy is already gated by CONFIG_HIGHMEM, otherwise >>> it needs to perform kmap_local() at each copying CPU, which complicates >>> the process. Then, this code will only used for 32bit without highmem, >>> I assume there will no page copy DMA on 32bit platform. Maybe it is not >>> too bad to limit this to 64bit. > > I agree. > >> >> I'm more concerned of CONFIG_64BIT handling in the code, but if that can be >> avoided easily, fine with me. > > > MIGRATION_COPY_OFFLOAD will not be enabled for !64BIT at config. > config MIGRATION_COPY_OFFLOAD > bool "Page migration copy offload" > depends on MIGRATION && 64BIT Might we worth documenting somewhere why, like ... > > I think only place in code we need #ifdef is: > enum { > FOLIO_WAS_MAPPED = BIT(0), > FOLIO_WAS_MLOCKED = BIT(1), > FOLIO_OLD_STATES = FOLIO_WAS_MAPPED | FOLIO_WAS_MLOCKED, > #ifdef CONFIG_MIGRATION_COPY_OFFLOAD > FOLIO_CONTENT_COPIED = BIT(2), > #else > FOLIO_CONTENT_COPIED = 0, ... here /* On 32bit we do not have a spare bit, migration-copy offload is disabled. */ > #endif > }; > > With FOLIO_CONTENT_COPIED=0, this will be no operation for its bit operation. > > eg: > const bool already_copied = dst->migrate_info & FOLIO_CONTENT_COPIED; > evaluates 0 for !64BIT. If that does the trick, good! -- Cheers, David