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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Karim Manaouil , Frank van der Linden , Teja Vojjala , Pravin Tamkhane , Kinsey Ho , Wei Xu , Matthew Wilcox , Davidlohr Bueso , Vinod Koul , Bharata B Rao , SeongJae Park , David Rientjes , Xuezheng Chu , Yiannis Nikolakopoulos , Dave Hansen , Johannes Weiner , John Hubbard , Peter Xu , Rik van Riel , Shakeel Butt , Tejun Heo , Fan Ni , Jonathan Cameron , "Aneesh Kumar K.V" , Nathan Lynch , Frank Li , Dan Williams , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Day Subject: Re: [PATCH RFC v6 3/5] mm/migrate: add copy offload registration infrastructure Date: Mon, 20 Jul 2026 10:44:34 -0400 X-Mailer: MailMate (3.0r7022) Message-ID: <19F47514-EBC4-4659-8252-EC3765D9B601@nvidia.com> In-Reply-To: <87wlupx60s.fsf@DESKTOP-5N7EMDA> References: <20260630-shivank-batch-migrate-offload-v6-0-da95d7e8b8a2@amd.com> <20260630-shivank-batch-migrate-offload-v6-3-da95d7e8b8a2@amd.com> 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-/* For now, never offload. Wired up in later patch. */ >> -static bool migrate_should_offload(int reason) >> -{ >> - return false; >> -} >> - >> static const struct movable_operations *offline_movable_ops; >> static const struct movable_operations *zsmalloc_movable_ops; >> >> @@ -2050,7 +2045,7 @@ static int migrate_pages_batch(struct list_head *from, >> >> /* Batch-copy eligible folios before the move phase */ >> if (!list_empty(&unmap_batch)) >> - migrate_folios_mc_copy(&dst_batch, &unmap_batch, nr_batch); >> + migrate_offload_batch_copy(&dst_batch, &unmap_batch, nr_batch); >> >> retry = 1; >> for (pass = 0; pass < nr_pass && retry; pass++) { > > Found a difference between v5 and v6 here. In v5, migrate_pages_batch() > checks the return value of migrate_offload_batch_copy() and acts > accordingly. While in v6, it does not. Why was this changed? > > IIUC, FOLIO_CONTENT_COPIED is now used to indicate a copy failure. Is > this necessary? Is it possible that some (but not all) folios fail to > be copied? Based on the discussion[1], FOLIO_CONTENT_COPIED is used to indicate both 1. folio is copied via offloading, and 2. MC copy failure. So the code no longer needs to store the return value of migrate_offload_batch_copy() and can just check dst->migrate_info & FOLIO_CONTENT_COPIED. For 32bit, FOLIO_CONTENT_COPIED is always 0, so all folios are always copied in the serialized path. Hmm, that might be causing double copying, since migrate_folios_mc_copy() copies batched folios and later migrate_folios_move() copies them again since dst->migrate_info & FOLIO_CONTENT_COPIED is always false. Maybe we could make migrate_folios_mc_copy() return immediately in 32bit, otherwise, we will need to find somewhere else to store FOLIO_CONTENT_COPIED. [1] https://lore.kernel.org/all/c2bfdf39-8caa-43bd-b1ad-2285b4cc767a@amd.com/ > > [snip] > > --- > Best Regards, > Huang, Ying Best Regards, Yan, Zi