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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7ebecb18cb4sm867878585a.2.2025.08.27.04.28.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Aug 2025 04:28:47 -0700 (PDT) Message-ID: <7cdc05d8-899b-495a-8298-ad5f27fcf8ad@redhat.com> Date: Wed, 27 Aug 2025 13:28:42 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [v3 02/11] mm/thp: zone_device awareness in THP handling code To: Balbir Singh , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Andrew Morton , Zi Yan , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Oscar Salvador , Lorenzo Stoakes , Baolin Wang , "Liam R. 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: 6do1k75ksa4sqe6y5ksoznnyng1rnxzb X-Rspam-User: X-Rspamd-Queue-Id: DDABC8000F X-Rspamd-Server: rspam01 X-HE-Tag: 1756294132-881248 X-HE-Meta: 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 /TJiNdC/ Xe81NMn1szklwWXnZqdCvwRHwrM7O0/iRwdruSy/j1ZIRNGR5rQXUS5amaR6DShCuCVMspVqKUnjA03SIWxjD8/XiK5oh5SAnPQrdK6EUdbjR0CghtUQ1db4UBrpbd8a6zHoq4TiP+p2hDYIv2cqwF7ClCIUDshvZ36KMJGRnMTytsGQQ1trev8Wj3LWjeQs87J1w19KBW4MS6pxNc38cmgbM6JdWM0PicceL7w6qka7OG/VbsouI5cxCBKcovflog4R7QUKD726WdwsFOuRINuXkfs9fVQgv3i4Sy861T5VW9BjxUACS1knoo1syju8FV9HSw6JgcnRu75iyiEs2qX/0axl3uaxANAHHS77lI2qKweyjv3yhri0pvMIPgqcfzzCVpKiljN6hAA/N7q+TSlwhuxS1PeevD8p7HziY0ZEAeygzEATzOjFVpl7ovU1P37wLjy3/pQmVUzqXJoyKdpleyS+K2lmbV9x/ItsLRgJ1TlU= 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: >> Like teaching zap, mprotect, rmap walks .... code separately. >> >> I'm, sure you'll find a way to break this down so I don't walk out of a >> review with an headake ;) >> > > :) I had smaller chunks earlier, but then ran into don't add the change unless you > use the change problem > It's perfectly reasonable to have something like mm/huge_memory: teach copy_huge_pmd() about huge device-private entries mm/huge_memory: support splitting device-private folios ... etc :) [...] >> Careful: There is is_readable_exclusive_migration_entry(). So don't >> change the !is_readable_migration_entry(entry) to is_writable_migration_entry(entry)(), >> because it's wrong. >> > > Ack, I assume you are referring to potential prot_none entries? readable_exclusive are used to maintain the PageAnonExclusive bit right now for migration entries. So it's not realted to prot_none. [...] >>> -            WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!"); >>> + >>> +            if (!thp_migration_supported()) >>> +                WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!"); >>> + >>> +            if (is_pmd_device_private_entry(orig_pmd)) { >>> +                folio_remove_rmap_pmd(folio, &folio->page, vma); >>> +                WARN_ON_ONCE(folio_mapcount(folio) < 0); >> >> Can we jsut move that into the folio_is_device_private() check below. > > The check you mean? The whole thing like if (...) { folio_remove_rmap_pmd(folio, &folio->page, vma); WARN_ON_ONCE(folio_mapcount(folio) < 0); folio_put(folio) } [...] > >> Why do we have to flush? pmd_clear() might be sufficient? In the PTE case we use pte_clear(). > > Without the flush, other entities will not see the cleared pmd and isn't the pte_clear() only > when should_defer_flush() is true? It's a non-present page entry, so there should be no TLB entry to flush. > >> >> [...] >> >>>           pmde = pmd_mksoft_dirty(pmde); >>>       if (is_writable_migration_entry(entry)) >>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c >>> index e05e14d6eacd..0ed337f94fcd 100644 >>> --- a/mm/migrate_device.c >>> +++ b/mm/migrate_device.c >>> @@ -136,6 +136,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, >>>                * page table entry. Other special swap entries are not >>>                * migratable, and we ignore regular swapped page. >>>                */ >>> +            struct folio *folio; >>> + >>>               entry = pte_to_swp_entry(pte); >>>               if (!is_device_private_entry(entry)) >>>                   goto next; >>> @@ -147,6 +149,51 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, >>>                   pgmap->owner != migrate->pgmap_owner) >>>                   goto next; >>>   +            folio = page_folio(page); >>> +            if (folio_test_large(folio)) { >>> +                struct folio *new_folio; >>> +                struct folio *new_fault_folio = NULL; >>> + >>> +                /* >>> +                 * The reason for finding pmd present with a >>> +                 * device private pte and a large folio for the >>> +                 * pte is partial unmaps. Split the folio now >>> +                 * for the migration to be handled correctly >>> +                 */ >> >> There are also other cases, like any VMA splits. Not sure if that makes a difference, >> the folio is PTE mapped. >> > > Ack, I can clarify that the folio is just pte mapped or remove the comment Sounds good. -- Cheers David / dhildenb