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t=1783918874; bh=4TsFRiFVI9paLB9M6jDRjv5Eb/d9Eu1NYpxkKiFfspY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GPf1tuml+sGCN4erdyJkNh515Ax5ndvBp7ZvsOztoJFR74RbbICpr5l2dYBlcm44d 6JBXkMbpVFnYz9oyBuUcJCpw41+2eFX2FGD7hM8hENqtC+mZDmzLj0eowTFRsG9AMT FMXjR097YRz3JLpDGpBY2qQFI/gTMBZJJhIW/GT8= From: Dev Jain To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, muchun.song@linux.dev, osalvador@suse.de Cc: Dev Jain , riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: [PATCH v3 2/5] mm/rmap: Add try_to_unmap_hugetlb_one Date: Mon, 13 Jul 2026 05:00:45 +0000 Message-ID: <20260713050050.1017741-3-dev.jain@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260713050050.1017741-1-dev.jain@arm.com> References: <20260713050050.1017741-1-dev.jain@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 21B4F20006 X-Stat-Signature: imyyc3gzw4y63x41tsax9szieqwfotmf X-HE-Tag: 1783918875-153965 X-HE-Meta: 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 wCzUL7jP qfywLGeiiaPhsOjN5ZB5Q+6KxzFPLugH0iPoXaBFeD3S5F3trF+koYBpt4MnHHo3KeIEf+XTgO4VZ6cjZTgbD5vTWTHuOCdPkuCC5b3mPYw6WfioKwRf5RbRDWjRIpyqd/pISIYqrZ4qUjYrhCOhXZw74uSFSeLsSFoohOlYxElGyYM/0FE/2FC3r7vMPWNWprldf19YkL3/fgKrO1J8SRlKKHfAQ602Xq30yhWMlV/ELGgYv/hGpls51qGXBXeVu03VaLktDHDNRhBYsqPSG9YTN4teo1+v092j+WlNx9R/nENENbmzJ+Hw4CIJhJDJBbJNv Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Simplify try_to_unmap_one() by separating the hugetlb parts into try_to_unmap_hugetlb_one(). To understand the correctness of the refactoring, the following points are noted: 1. try_to_unmap() is called for hugetlb folios only when they are hwpoisoned. 2. A hugetlb VMA cannot be mlocked. 3. page_vma_mapped_walk() returns at most one hugetlb mapping in a VMA, and that mapping points at the head PFN. 4. We won't ever process a softleaf entry that encodes a hugetlb folio; hugetlb folios are never swapped out, migration entries will be skipped (PVMW_MIGRATION not passed), and device-exclusive does not work for hugetlb. 5. The hwpoison entry is constructed from the poisoned folio, just as in the pre-refactor code. Any previous uffd-wp state is deliberately not preserved for the hwpoison entry. 6. TTU_HWPOISON is always present; for it to not be present, either the folio has to be in swapcache, or mapping_can_writeback() is true (see unmap_poisoned_folio), none of which is true for hugetlb folios. 7. Hugetlb uses separate counters from normal rss counters, therefore update_highwater_rss() need not be called. While at it: - Change VM_BUG_* to VM_WARN_*. - Do not declare variables which are only used once. - Constify some variables. - Add some more VM_WARN_* to assert some invariants. Except the above 4 points, no functional change intended. Suggested-by: David Hildenbrand (Arm) Acked-by: David Hildenbrand (Arm) Signed-off-by: Dev Jain --- include/linux/hugetlb.h | 1 + mm/rmap.c | 183 +++++++++++++++++++++------------------- 2 files changed, 98 insertions(+), 86 deletions(-) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 4115076e4922a..bf7e163e3779d 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -1271,6 +1271,7 @@ static inline void hugetlb_count_sub(long l, struct mm_struct *mm) } pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep); +unsigned long huge_pte_dirty(pte_t pte); static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep) diff --git a/mm/rmap.c b/mm/rmap.c index 2b74668f356d6..7720c49ada4c3 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1978,6 +1978,96 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio, FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY); } +static bool try_to_unmap_hugetlb_one(struct folio *folio, + struct vm_area_struct *vma, unsigned long address, void *arg) +{ + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); + const unsigned long hsz = huge_page_size(hstate_vma(vma)); + const enum ttu_flags flags = (enum ttu_flags)(long)arg; + struct mm_struct *mm = vma->vm_mm; + struct mmu_notifier_range range; + bool ret = true; + pte_t pteval; + + /* + * The try_to_unmap() is only passed a hugetlb folio in the case + * where the hugetlb folio is poisoned. + */ + VM_WARN_ON_FOLIO(!folio_test_hwpoison(folio), folio); + VM_WARN_ON_ONCE(!(flags & TTU_HWPOISON)); + + range.end = vma_address_end(&pvmw); + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm, + address, range.end); + adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end); + mmu_notifier_invalidate_range_start(&range); + + /* There is only a single mapping in a VMA. */ + if (!page_vma_mapped_walk(&pvmw)) + goto range_end; + + VM_WARN_ON_ONCE(address != pvmw.address); + + pteval = huge_ptep_get(mm, address, pvmw.pte); + VM_WARN_ON_ONCE(!pte_present(pteval)); + VM_WARN_ON_ONCE(pte_pfn(pteval) != folio_pfn(folio)); + + /* + * huge_pmd_unshare may unmap an entire PMD page. There is no way of + * knowing exactly which PMDs may be cached for this mm, so we must + * flush them all. start/end were already adjusted above to cover this + * range. + */ + flush_cache_range(vma, range.start, range.end); + + /* + * To call huge_pmd_unshare, i_mmap_rwsem must be held in write mode. + * Caller needs to explicitly do this outside rmap routines. + * + * We also must hold hugetlb vma_lock in write mode. Lock order dictates + * acquiring vma_lock BEFORE i_mmap_rwsem. We can only try lock here and + * fail if unsuccessful. + */ + if (!folio_test_anon(folio)) { + struct mmu_gather tlb; + + VM_WARN_ON(!(flags & TTU_RMAP_LOCKED)); + if (!hugetlb_vma_trylock_write(vma)) { + ret = false; + goto walk_done; + } + + tlb_gather_mmu_vma(&tlb, vma); + if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) { + hugetlb_vma_unlock_write(vma); + huge_pmd_unshare_flush(&tlb, vma); + tlb_finish_mmu(&tlb); + /* + * The PMD table was unmapped, consequently unmapping + * the folio. + */ + goto walk_done; + } + hugetlb_vma_unlock_write(vma); + tlb_finish_mmu(&tlb); + } + pteval = huge_ptep_clear_flush(vma, address, pvmw.pte); + if (huge_pte_dirty(pteval)) + folio_mark_dirty(folio); + + pteval = swp_entry_to_pte(make_hwpoison_entry(folio_page(folio, 0))); + hugetlb_count_sub(folio_nr_pages(folio), mm); + set_huge_pte_at(mm, address, pvmw.pte, pteval, hsz); + hugetlb_remove_rmap(folio); + folio_put_refs(folio, 1); + +walk_done: + page_vma_mapped_walk_done(&pvmw); +range_end: + mmu_notifier_invalidate_range_end(&range); + return ret; +} + /* * @arg: enum ttu_flags will be passed to this argument */ @@ -1993,7 +2083,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, enum ttu_flags flags = (enum ttu_flags)(long)arg; unsigned long nr_pages = 1, end_addr; unsigned long pfn; - unsigned long hsz = 0; int ptes = 0; /* @@ -2007,8 +2096,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, /* * For THP, we have to assume the worse case ie pmd for invalidation. - * For hugetlb, it could be much worse if we need to do pud - * invalidation in the case of pmd sharing. * * Note that the folio can not be freed in this function as call of * try_to_unmap() must hold a reference on the folio. @@ -2016,17 +2103,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, range.end = vma_address_end(&pvmw); mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm, address, range.end); - if (folio_test_hugetlb(folio)) { - /* - * If sharing is possible, start and end will be adjusted - * accordingly. - */ - adjust_range_if_pmd_sharing_possible(vma, &range.start, - &range.end); - - /* We need the huge page size for set_huge_pte_at() */ - hsz = huge_page_size(hstate_vma(vma)); - } mmu_notifier_invalidate_range_start(&range); while (page_vma_mapped_walk(&pvmw)) { @@ -2111,66 +2187,13 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, const softleaf_t entry = softleaf_from_pte(pteval); pfn = softleaf_to_pfn(entry); - VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio); } subpage = folio_page(folio, pfn - folio_pfn(folio)); anon_exclusive = folio_test_anon(folio) && PageAnonExclusive(subpage); - if (folio_test_hugetlb(folio)) { - bool anon = folio_test_anon(folio); - - /* - * The try_to_unmap() is only passed a hugetlb folio - * in the case where the hugetlb folio contains a - * poisoned page. - */ - VM_WARN_ON_FOLIO(!folio_test_hwpoison(folio), folio); - /* - * huge_pmd_unshare may unmap an entire PMD page. - * There is no way of knowing exactly which PMDs may - * be cached for this mm, so we must flush them all. - * start/end were already adjusted above to cover this - * range. - */ - flush_cache_range(vma, range.start, range.end); - - /* - * To call huge_pmd_unshare, i_mmap_rwsem must be - * held in write mode. Caller needs to explicitly - * do this outside rmap routines. - * - * We also must hold hugetlb vma_lock in write mode. - * Lock order dictates acquiring vma_lock BEFORE - * i_mmap_rwsem. We can only try lock here and fail - * if unsuccessful. - */ - if (!anon) { - struct mmu_gather tlb; - - VM_BUG_ON(!(flags & TTU_RMAP_LOCKED)); - if (!hugetlb_vma_trylock_write(vma)) - goto walk_abort; - - tlb_gather_mmu_vma(&tlb, vma); - if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) { - hugetlb_vma_unlock_write(vma); - huge_pmd_unshare_flush(&tlb, vma); - tlb_finish_mmu(&tlb); - /* - * The PMD table was unmapped, - * consequently unmapping the folio. - */ - goto walk_done; - } - hugetlb_vma_unlock_write(vma); - tlb_finish_mmu(&tlb); - } - pteval = huge_ptep_clear_flush(vma, address, pvmw.pte); - if (pte_dirty(pteval)) - folio_mark_dirty(folio); - } else if (likely(pte_present(pteval))) { + if (likely(pte_present(pteval))) { nr_pages = folio_unmap_pte_batch(folio, &pvmw, flags, pteval); end_addr = address + nr_pages * PAGE_SIZE; flush_cache_range(vma, address, end_addr); @@ -2205,20 +2228,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, /* Update high watermark before we lower rss */ update_hiwater_rss(mm); - /* - * With TTU_HWPOISON, we only expect small folios or hugetlb - * folios here for now. - */ + /* With TTU_HWPOISON, we only expect small folios here. */ if (folio_test_hwpoison(folio) && (flags & TTU_HWPOISON)) { pteval = swp_entry_to_pte(make_hwpoison_entry(subpage)); - if (folio_test_hugetlb(folio)) { - hugetlb_count_sub(folio_nr_pages(folio), mm); - set_huge_pte_at(mm, address, pvmw.pte, pteval, - hsz); - } else { - dec_mm_counter(mm, mm_counter(folio)); - set_pte_at(mm, address, pvmw.pte, pteval); - } + dec_mm_counter(mm, mm_counter(folio)); + set_pte_at(mm, address, pvmw.pte, pteval); } else if (likely(pte_present(pteval)) && pte_unused(pteval) && !userfaultfd_armed(vma)) { /* @@ -2346,11 +2360,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, add_mm_counter(mm, mm_counter_file(folio), -nr_pages); } discard: - if (unlikely(folio_test_hugetlb(folio))) { - hugetlb_remove_rmap(folio); - } else { - folio_remove_rmap_ptes(folio, subpage, nr_pages, vma); - } + folio_remove_rmap_ptes(folio, subpage, nr_pages, vma); if (vma->vm_flags & VM_LOCKED) mlock_drain_local(); folio_put_refs(folio, nr_pages); @@ -2398,7 +2408,8 @@ static int folio_not_mapped(struct folio *folio) void try_to_unmap(struct folio *folio, enum ttu_flags flags) { struct rmap_walk_control rwc = { - .rmap_one = try_to_unmap_one, + .rmap_one = folio_test_hugetlb(folio) ? + try_to_unmap_hugetlb_one : try_to_unmap_one, .arg = (void *)flags, .done = folio_not_mapped, .anon_lock = folio_lock_anon_vma_read, -- 2.43.0