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Sun, 28 Dec 2025 14:07:49 -0800 (PST) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org Cc: 21cnbao@gmail.com, chrisl@kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, wale.zhang.ftd@gmail.com Subject: Re: [PATCH 1/1] mm,swapops: Fix compile error on set_pmd_migration_entry. Date: Mon, 29 Dec 2025 11:07:41 +1300 Message-ID: <20251228220742.11157-1-21cnbao@gmail.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20251228133742.a1f90fc552d346c4c43aad8b@linux-foundation.org> References: <20251228133742.a1f90fc552d346c4c43aad8b@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 6701D180003 X-Stat-Signature: ykeow9z9bmyjy8u4oy1nzeqjcij1rbrq X-HE-Tag: 1766959671-312168 X-HE-Meta: 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 7g2PNkUI 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 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: On Mon, Dec 29, 2025 at 10:37 AM Andrew Morton wrote: > > On Sat, 27 Dec 2025 17:58:40 +0800 wale zhang wrote: > > > > No. You still don’t understand my point. The BUILD_BUG means this > > > code will never have a chance to be compiled under any possible > > > kernel configuration. That makes it dead code. If there is any > > > kernel .config in which it can be built, then we should fix it. > > > > > > This set_pmd_migration_entry() has no chance of ever being built. > > > > Hello Barry, > > > > Please share the .config which was used to trigger this build error. > > (It is strange to have this should-never-be-compiled code.  Why not just > delete it and let the compiler/linker report the error.) Right. We should entirely drop it in mainline. If Wale does want an O0 build, then the only call to set_pmd_migration_entry() that is not under #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION is migrate_vma_collect_huge_pmd() in mm/migrate_device.c. Then what we really need is as follows: diff --git a/include/linux/swapops.h b/include/linux/swapops.h index 8cfc966eae48..fdd4375d5d90 100644 --- a/include/linux/swapops.h +++ b/include/linux/swapops.h @@ -339,17 +339,6 @@ static inline pmd_t swp_entry_to_pmd(swp_entry_t entry) } #else /* CONFIG_ARCH_ENABLE_THP_MIGRATION */ -static inline int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, - struct page *page) -{ - BUILD_BUG(); -} - -static inline void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, - struct page *new) -{ - BUILD_BUG(); -} static inline void pmd_migration_entry_wait(struct mm_struct *m, pmd_t *p) { } diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 23379663b1e1..74d23c91626a 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -195,8 +195,9 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start, return migrate_vma_collect_skip(start, end, walk); } - if (thp_migration_supported() && - (migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) && + +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION + if ((migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) && (IS_ALIGNED(start, HPAGE_PMD_SIZE) && IS_ALIGNED(end, HPAGE_PMD_SIZE))) { @@ -226,6 +227,7 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start, spin_unlock(ptl); return 0; } +#endif fallback: spin_unlock(ptl); Thanks Barry