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Fri, 14 Feb 2025 01:30:36 -0800 (PST) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: 21cnbao@gmail.com, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, ioworker0@gmail.com, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, ying.huang@intel.com, zhengtangquan@oppo.com, Mauricio Faria de Oliveira Subject: [PATCH v4 1/4] mm: Set folio swapbacked iff folios are dirty in try_to_unmap_one Date: Fri, 14 Feb 2025 22:30:12 +1300 Message-Id: <20250214093015.51024-2-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20250214093015.51024-1-21cnbao@gmail.com> References: <20250214093015.51024-1-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Barry Song The refcount may be temporarily or long-term increased, but this does not change the fundamental nature of the folio already being lazy- freed. Therefore, we only reset 'swapbacked' when we are certain the folio is dirty and not droppable. Fixes: 6c8e2a256915 ("mm: fix race between MADV_FREE reclaim and blkdev dir= ect IO read") Suggested-by: David Hildenbrand Signed-off-by: Barry Song Cc: Mauricio Faria de Oliveira Acked-by: David Hildenbrand Reviewed-by: Baolin Wang Reviewed-by: Lance Yang --- mm/rmap.c | 49 ++++++++++++++++++++++--------------------------- 1 file changed, 22 insertions(+), 27 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index 25a8a127f689..1320527e90cd 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -2022,34 +2022,29 @@ static bool try_to_unmap_one(struct folio *folio, s= truct vm_area_struct *vma, */ smp_rmb(); =20 - /* - * The only page refs must be one from isolation - * plus the rmap(s) (dropped by discard:). - */ - if (ref_count =3D=3D 1 + map_count && - (!folio_test_dirty(folio) || - /* - * Unlike MADV_FREE mappings, VM_DROPPABLE - * ones can be dropped even if they've - * been dirtied. - */ - (vma->vm_flags & VM_DROPPABLE))) { - dec_mm_counter(mm, MM_ANONPAGES); - goto discard; - } - - /* - * If the folio was redirtied, it cannot be - * discarded. Remap the page to page table. - */ - set_pte_at(mm, address, pvmw.pte, pteval); - /* - * Unlike MADV_FREE mappings, VM_DROPPABLE ones - * never get swap backed on failure to drop. - */ - if (!(vma->vm_flags & VM_DROPPABLE)) + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { + /* + * redirtied either using the page table or a previously + * obtained GUP reference. + */ + set_pte_at(mm, address, pvmw.pte, pteval); folio_set_swapbacked(folio); - goto walk_abort; + goto walk_abort; + } else if (ref_count !=3D 1 + map_count) { + /* + * Additional reference. Could be a GUP reference or any + * speculative reference. GUP users must mark the folio + * dirty if there was a modification. This folio cannot be + * reclaimed right now either way, so act just like nothing + * happened. + * We'll come back here later and detect if the folio was + * dirtied when the additional reference is gone. + */ + set_pte_at(mm, address, pvmw.pte, pteval); + goto walk_abort; + } + dec_mm_counter(mm, MM_ANONPAGES); + goto discard; } =20 if (swap_duplicate(entry) < 0) { --=20 2.39.3 (Apple Git-146) From nobody Wed Mar 12 23:48:56 2025 Received: from mail-pl1-f173.google.com (mail-pl1-f173.google.com [209.85.214.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AEA9418FDBD for ; Fri, 14 Feb 2025 09:30:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.173 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739525451; cv=none; b=UEET8g0vaahMxT30IIXbu8PqThRW0m+Bc9+O6hHL+7MLKYM1hNqGQiimqIsF5emBCD/RoIrLxPeYApQuifXvqhnco0XPvi9cP0tkgYUybak5hp6Onc9c+j2xwb7kQihPuae2AZgmLyPuH9t6Oihx3OnIKj5Vtx4LoJNchmzRJUY= ARC-Message-Signature: i=1; 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Fri, 14 Feb 2025 01:30:48 -0800 (PST) Received: from Barrys-MBP.hub ([118.92.30.135]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-220d545c814sm25440515ad.148.2025.02.14.01.30.37 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 14 Feb 2025 01:30:48 -0800 (PST) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: 21cnbao@gmail.com, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, ioworker0@gmail.com, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, ying.huang@intel.com, zhengtangquan@oppo.com, Catalin Marinas , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Anshuman Khandual , Shaoqin Huang , Gavin Shan , Mark Rutland , "Kirill A. Shutemov" , Yosry Ahmed , Paul Walmsley , Palmer Dabbelt , Albert Ou , Yicong Yang , Will Deacon , Kefeng Wang Subject: [PATCH v4 2/4] mm: Support tlbbatch flush for a range of PTEs Date: Fri, 14 Feb 2025 22:30:13 +1300 Message-Id: <20250214093015.51024-3-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20250214093015.51024-1-21cnbao@gmail.com> References: <20250214093015.51024-1-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Barry Song This patch lays the groundwork for supporting batch PTE unmapping in try_to_unmap_one(). It introduces range handling for TLB batch flushing, with the range currently set to the size of PAGE_SIZE. The function __flush_tlb_range_nosync() is architecture-specific and is only used within arch/arm64. This function requires the mm structure instead of the vma structure. To allow its reuse by arch_tlbbatch_add_pending(), which operates with mm but not vma, this patch modifies the argument of __flush_tlb_range_nosync() to take mm as its parameter. Cc: Catalin Marinas Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: Anshuman Khandual Cc: Ryan Roberts Cc: Shaoqin Huang Cc: Gavin Shan Cc: Mark Rutland Cc: David Hildenbrand Cc: Lance Yang Cc: "Kirill A. Shutemov" Cc: Yosry Ahmed Cc: Paul Walmsley Cc: Palmer Dabbelt Cc: Albert Ou Cc: Yicong Yang Signed-off-by: Barry Song Acked-by: Will Deacon Reviewed-by: Kefeng Wang --- arch/arm64/include/asm/tlbflush.h | 23 +++++++++++------------ arch/arm64/mm/contpte.c | 2 +- arch/riscv/include/asm/tlbflush.h | 3 +-- arch/riscv/mm/tlbflush.c | 3 +-- arch/x86/include/asm/tlbflush.h | 3 +-- mm/rmap.c | 10 +++++----- 6 files changed, 20 insertions(+), 24 deletions(-) diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlb= flush.h index bc94e036a26b..b7e1920570bd 100644 --- a/arch/arm64/include/asm/tlbflush.h +++ b/arch/arm64/include/asm/tlbflush.h @@ -322,13 +322,6 @@ static inline bool arch_tlbbatch_should_defer(struct m= m_struct *mm) return true; } =20 -static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_ba= tch *batch, - struct mm_struct *mm, - unsigned long uaddr) -{ - __flush_tlb_page_nosync(mm, uaddr); -} - /* * If mprotect/munmap/etc occurs during TLB batched flushing, we need to * synchronise all the TLBI issued with a DSB to avoid the race mentioned = in @@ -448,7 +441,7 @@ static inline bool __flush_tlb_range_limit_excess(unsig= ned long start, return false; } =20 -static inline void __flush_tlb_range_nosync(struct vm_area_struct *vma, +static inline void __flush_tlb_range_nosync(struct mm_struct *mm, unsigned long start, unsigned long end, unsigned long stride, bool last_level, int tlb_level) @@ -460,12 +453,12 @@ static inline void __flush_tlb_range_nosync(struct vm= _area_struct *vma, pages =3D (end - start) >> PAGE_SHIFT; =20 if (__flush_tlb_range_limit_excess(start, end, pages, stride)) { - flush_tlb_mm(vma->vm_mm); + flush_tlb_mm(mm); return; } =20 dsb(ishst); - asid =3D ASID(vma->vm_mm); + asid =3D ASID(mm); =20 if (last_level) __flush_tlb_range_op(vale1is, start, pages, stride, asid, @@ -474,7 +467,7 @@ static inline void __flush_tlb_range_nosync(struct vm_a= rea_struct *vma, __flush_tlb_range_op(vae1is, start, pages, stride, asid, tlb_level, true, lpa2_is_enabled()); =20 - mmu_notifier_arch_invalidate_secondary_tlbs(vma->vm_mm, start, end); + mmu_notifier_arch_invalidate_secondary_tlbs(mm, start, end); } =20 static inline void __flush_tlb_range(struct vm_area_struct *vma, @@ -482,7 +475,7 @@ static inline void __flush_tlb_range(struct vm_area_str= uct *vma, unsigned long stride, bool last_level, int tlb_level) { - __flush_tlb_range_nosync(vma, start, end, stride, + __flush_tlb_range_nosync(vma->vm_mm, start, end, stride, last_level, tlb_level); dsb(ish); } @@ -533,6 +526,12 @@ static inline void __flush_tlb_kernel_pgtable(unsigned= long kaddr) dsb(ish); isb(); } + +static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_ba= tch *batch, + struct mm_struct *mm, unsigned long start, unsigned long end) +{ + __flush_tlb_range_nosync(mm, start, end, PAGE_SIZE, true, 3); +} #endif =20 #endif diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c index 55107d27d3f8..bcac4f55f9c1 100644 --- a/arch/arm64/mm/contpte.c +++ b/arch/arm64/mm/contpte.c @@ -335,7 +335,7 @@ int contpte_ptep_clear_flush_young(struct vm_area_struc= t *vma, * eliding the trailing DSB applies here. */ addr =3D ALIGN_DOWN(addr, CONT_PTE_SIZE); - __flush_tlb_range_nosync(vma, addr, addr + CONT_PTE_SIZE, + __flush_tlb_range_nosync(vma->vm_mm, addr, addr + CONT_PTE_SIZE, PAGE_SIZE, true, 3); } =20 diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlb= flush.h index 72e559934952..ce0dd0fed764 100644 --- a/arch/riscv/include/asm/tlbflush.h +++ b/arch/riscv/include/asm/tlbflush.h @@ -60,8 +60,7 @@ void flush_pmd_tlb_range(struct vm_area_struct *vma, unsi= gned long start, =20 bool arch_tlbbatch_should_defer(struct mm_struct *mm); void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch, - struct mm_struct *mm, - unsigned long uaddr); + struct mm_struct *mm, unsigned long start, unsigned long end); void arch_flush_tlb_batched_pending(struct mm_struct *mm); void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch); =20 diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c index 9b6e86ce3867..74dd9307fbf1 100644 --- a/arch/riscv/mm/tlbflush.c +++ b/arch/riscv/mm/tlbflush.c @@ -186,8 +186,7 @@ bool arch_tlbbatch_should_defer(struct mm_struct *mm) } =20 void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch, - struct mm_struct *mm, - unsigned long uaddr) + struct mm_struct *mm, unsigned long start, unsigned long end) { cpumask_or(&batch->cpumask, &batch->cpumask, mm_cpumask(mm)); } diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflus= h.h index 02fc2aa06e9e..29373da7b00a 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -279,8 +279,7 @@ static inline u64 inc_mm_tlb_gen(struct mm_struct *mm) } =20 static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_ba= tch *batch, - struct mm_struct *mm, - unsigned long uaddr) + struct mm_struct *mm, unsigned long start, unsigned long end) { inc_mm_tlb_gen(mm); cpumask_or(&batch->cpumask, &batch->cpumask, mm_cpumask(mm)); diff --git a/mm/rmap.c b/mm/rmap.c index 1320527e90cd..89e51a7a9509 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -672,7 +672,7 @@ void try_to_unmap_flush_dirty(void) (TLB_FLUSH_BATCH_PENDING_MASK / 2) =20 static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval, - unsigned long uaddr) + unsigned long start, unsigned long end) { struct tlbflush_unmap_batch *tlb_ubc =3D ¤t->tlb_ubc; int batch; @@ -681,7 +681,7 @@ static void set_tlb_ubc_flush_pending(struct mm_struct = *mm, pte_t pteval, if (!pte_accessible(mm, pteval)) return; =20 - arch_tlbbatch_add_pending(&tlb_ubc->arch, mm, uaddr); + arch_tlbbatch_add_pending(&tlb_ubc->arch, mm, start, end); tlb_ubc->flush_required =3D true; =20 /* @@ -757,7 +757,7 @@ void flush_tlb_batched_pending(struct mm_struct *mm) } #else static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval, - unsigned long uaddr) + unsigned long start, unsigned long end) { } =20 @@ -1946,7 +1946,7 @@ static bool try_to_unmap_one(struct folio *folio, str= uct vm_area_struct *vma, */ pteval =3D ptep_get_and_clear(mm, address, pvmw.pte); 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Fri, 14 Feb 2025 01:30:55 -0800 (PST) Received: from Barrys-MBP.hub ([118.92.30.135]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-220d545c814sm25440515ad.148.2025.02.14.01.30.49 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 14 Feb 2025 01:30:54 -0800 (PST) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: 21cnbao@gmail.com, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, ioworker0@gmail.com, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, ying.huang@intel.com, zhengtangquan@oppo.com Subject: [PATCH v4 3/4] mm: Support batched unmap for lazyfree large folios during reclamation Date: Fri, 14 Feb 2025 22:30:14 +1300 Message-Id: <20250214093015.51024-4-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20250214093015.51024-1-21cnbao@gmail.com> References: <20250214093015.51024-1-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Barry Song Currently, the PTEs and rmap of a large folio are removed one at a time. This is not only slow but also causes the large folio to be unnecessarily added to deferred_split, which can lead to races between the deferred_split shrinker callback and memory reclamation. This patch releases all PTEs and rmap entries in a batch. Currently, it only handles lazyfree large folios. The below microbench tries to reclaim 128MB lazyfree large folios whose sizes are 64KiB: #include #include #include #include #define SIZE 128*1024*1024 // 128 MB unsigned long read_split_deferred() { FILE *file =3D fopen("/sys/kernel/mm/transparent_hugepage" "/hugepages-64kB/stats/split_deferred", "r"); if (!file) { perror("Error opening file"); return 0; } unsigned long value; if (fscanf(file, "%lu", &value) !=3D 1) { perror("Error reading value"); fclose(file); return 0; } fclose(file); return value; } int main(int argc, char *argv[]) { while(1) { volatile int *p =3D mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); memset((void *)p, 1, SIZE); madvise((void *)p, SIZE, MADV_FREE); clock_t start_time =3D clock(); unsigned long start_split =3D read_split_deferred(); madvise((void *)p, SIZE, MADV_PAGEOUT); clock_t end_time =3D clock(); unsigned long end_split =3D read_split_deferred(); double elapsed_time =3D (double)(end_time - start_time) / CLOCKS_PER_SEC; printf("Time taken by reclamation: %f seconds, split_deferred: %ld\n", elapsed_time, end_split - start_split); munmap((void *)p, SIZE); } return 0; } w/o patch: ~ # ./a.out Time taken by reclamation: 0.177418 seconds, split_deferred: 2048 Time taken by reclamation: 0.178348 seconds, split_deferred: 2048 Time taken by reclamation: 0.174525 seconds, split_deferred: 2048 Time taken by reclamation: 0.171620 seconds, split_deferred: 2048 Time taken by reclamation: 0.172241 seconds, split_deferred: 2048 Time taken by reclamation: 0.174003 seconds, split_deferred: 2048 Time taken by reclamation: 0.171058 seconds, split_deferred: 2048 Time taken by reclamation: 0.171993 seconds, split_deferred: 2048 Time taken by reclamation: 0.169829 seconds, split_deferred: 2048 Time taken by reclamation: 0.172895 seconds, split_deferred: 2048 Time taken by reclamation: 0.176063 seconds, split_deferred: 2048 Time taken by reclamation: 0.172568 seconds, split_deferred: 2048 Time taken by reclamation: 0.171185 seconds, split_deferred: 2048 Time taken by reclamation: 0.170632 seconds, split_deferred: 2048 Time taken by reclamation: 0.170208 seconds, split_deferred: 2048 Time taken by reclamation: 0.174192 seconds, split_deferred: 2048 ... w/ patch: ~ # ./a.out Time taken by reclamation: 0.074231 seconds, split_deferred: 0 Time taken by reclamation: 0.071026 seconds, split_deferred: 0 Time taken by reclamation: 0.072029 seconds, split_deferred: 0 Time taken by reclamation: 0.071873 seconds, split_deferred: 0 Time taken by reclamation: 0.073573 seconds, split_deferred: 0 Time taken by reclamation: 0.071906 seconds, split_deferred: 0 Time taken by reclamation: 0.073604 seconds, split_deferred: 0 Time taken by reclamation: 0.075903 seconds, split_deferred: 0 Time taken by reclamation: 0.073191 seconds, split_deferred: 0 Time taken by reclamation: 0.071228 seconds, split_deferred: 0 Time taken by reclamation: 0.071391 seconds, split_deferred: 0 Time taken by reclamation: 0.071468 seconds, split_deferred: 0 Time taken by reclamation: 0.071896 seconds, split_deferred: 0 Time taken by reclamation: 0.072508 seconds, split_deferred: 0 Time taken by reclamation: 0.071884 seconds, split_deferred: 0 Time taken by reclamation: 0.072433 seconds, split_deferred: 0 Time taken by reclamation: 0.071939 seconds, split_deferred: 0 ... Signed-off-by: Barry Song --- mm/rmap.c | 72 ++++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 50 insertions(+), 22 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index 89e51a7a9509..8786704bd466 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1781,6 +1781,25 @@ void folio_remove_rmap_pud(struct folio *folio, stru= ct page *page, #endif } =20 +/* We support batch unmapping of PTEs for lazyfree large folios */ +static inline bool can_batch_unmap_folio_ptes(unsigned long addr, + struct folio *folio, pte_t *ptep) +{ + const fpb_t fpb_flags =3D FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; + int max_nr =3D folio_nr_pages(folio); + pte_t pte =3D ptep_get(ptep); + + if (!folio_test_anon(folio) || folio_test_swapbacked(folio)) + return false; + if (pte_unused(pte)) + return false; + if (pte_pfn(pte) !=3D folio_pfn(folio)) + return false; + + return folio_pte_batch(folio, addr, ptep, pte, max_nr, fpb_flags, NULL, + NULL, NULL) =3D=3D max_nr; +} + /* * @arg: enum ttu_flags will be passed to this argument */ @@ -1794,6 +1813,7 @@ static bool try_to_unmap_one(struct folio *folio, str= uct vm_area_struct *vma, struct page *subpage; struct mmu_notifier_range range; enum ttu_flags flags =3D (enum ttu_flags)(long)arg; + unsigned long nr_pages =3D 1, end_addr; unsigned long pfn; unsigned long hsz =3D 0; =20 @@ -1933,23 +1953,26 @@ static bool try_to_unmap_one(struct folio *folio, s= truct vm_area_struct *vma, if (pte_dirty(pteval)) folio_mark_dirty(folio); } else if (likely(pte_present(pteval))) { - flush_cache_page(vma, address, pfn); - /* Nuke the page table entry. */ - if (should_defer_flush(mm, flags)) { - /* - * We clear the PTE but do not flush so potentially - * a remote CPU could still be writing to the folio. - * If the entry was previously clean then the - * architecture must guarantee that a clear->dirty - * transition on a cached TLB entry is written through - * and traps if the PTE is unmapped. - */ - pteval =3D ptep_get_and_clear(mm, address, pvmw.pte); + if (folio_test_large(folio) && !(flags & TTU_HWPOISON) && + can_batch_unmap_folio_ptes(address, folio, pvmw.pte)) + nr_pages =3D folio_nr_pages(folio); + end_addr =3D address + nr_pages * PAGE_SIZE; + flush_cache_range(vma, address, end_addr); =20 - set_tlb_ubc_flush_pending(mm, pteval, address, address + PAGE_SIZE); - } else { - pteval =3D ptep_clear_flush(vma, address, pvmw.pte); - } + /* Nuke the page table entry. */ + pteval =3D get_and_clear_full_ptes(mm, address, pvmw.pte, nr_pages, 0); + /* + * We clear the PTE but do not flush so potentially + * a remote CPU could still be writing to the folio. + * If the entry was previously clean then the + * architecture must guarantee that a clear->dirty + * transition on a cached TLB entry is written through + * and traps if the PTE is unmapped. + */ + if (should_defer_flush(mm, flags)) + set_tlb_ubc_flush_pending(mm, pteval, address, end_addr); + else + flush_tlb_range(vma, address, end_addr); if (pte_dirty(pteval)) folio_mark_dirty(folio); } else { @@ -2027,7 +2050,7 @@ static bool try_to_unmap_one(struct folio *folio, str= uct vm_area_struct *vma, * redirtied either using the page table or a previously * obtained GUP reference. */ - set_pte_at(mm, address, pvmw.pte, pteval); + set_ptes(mm, address, pvmw.pte, pteval, nr_pages); folio_set_swapbacked(folio); goto walk_abort; } else if (ref_count !=3D 1 + map_count) { @@ -2040,10 +2063,10 @@ static bool try_to_unmap_one(struct folio *folio, s= truct vm_area_struct *vma, * We'll come back here later and detect if the folio was * dirtied when the additional reference is gone. */ - set_pte_at(mm, address, pvmw.pte, pteval); + set_ptes(mm, address, pvmw.pte, pteval, nr_pages); goto walk_abort; } - dec_mm_counter(mm, MM_ANONPAGES); + add_mm_counter(mm, MM_ANONPAGES, -nr_pages); goto discard; } =20 @@ -2108,13 +2131,18 @@ static bool try_to_unmap_one(struct folio *folio, s= truct vm_area_struct *vma, dec_mm_counter(mm, mm_counter_file(folio)); } discard: - if (unlikely(folio_test_hugetlb(folio))) + if (unlikely(folio_test_hugetlb(folio))) { hugetlb_remove_rmap(folio); - else - folio_remove_rmap_pte(folio, subpage, vma); + } else { + folio_remove_rmap_ptes(folio, subpage, nr_pages, vma); + folio_ref_sub(folio, nr_pages - 1); 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Fri, 14 Feb 2025 01:31:01 -0800 (PST) Received: from Barrys-MBP.hub ([118.92.30.135]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-220d545c814sm25440515ad.148.2025.02.14.01.30.55 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 14 Feb 2025 01:31:01 -0800 (PST) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: 21cnbao@gmail.com, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, ioworker0@gmail.com, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, ying.huang@intel.com, zhengtangquan@oppo.com Subject: [PATCH v4 4/4] mm: Avoid splitting pmd for lazyfree pmd-mapped THP in try_to_unmap Date: Fri, 14 Feb 2025 22:30:15 +1300 Message-Id: <20250214093015.51024-5-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20250214093015.51024-1-21cnbao@gmail.com> References: <20250214093015.51024-1-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable From: Barry Song The try_to_unmap_one() function currently handles PMD-mapped THPs inefficiently. It first splits the PMD into PTEs, copies the dirty state from the PMD to the PTEs, iterates over the PTEs to locate the dirty state, and then marks the THP as swap-backed. This process involves unnecessary PMD splitting and redundant iteration. Instead, this functionality can be efficiently managed in __discard_anon_folio_pmd_locked(), avoiding the extra steps and improving performance. The following microbenchmark redirties folios after invoking MADV_FREE, then measures the time taken to perform memory reclamation (actually set those folios swapbacked again) on the redirtied folios. #include #include #include #include #define SIZE 128*1024*1024 // 128 MB int main(int argc, char *argv[]) { while(1) { volatile int *p =3D mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); memset((void *)p, 1, SIZE); madvise((void *)p, SIZE, MADV_FREE); /* redirty after MADV_FREE */ memset((void *)p, 1, SIZE); clock_t start_time =3D clock(); madvise((void *)p, SIZE, MADV_PAGEOUT); clock_t end_time =3D clock(); double elapsed_time =3D (double)(end_time - start_time) / CLOCKS_PER_SEC; printf("Time taken by reclamation: %f seconds\n", elapsed_time); munmap((void *)p, SIZE); } return 0; } Testing results are as below, w/o patch: ~ # ./a.out Time taken by reclamation: 0.007300 seconds Time taken by reclamation: 0.007226 seconds Time taken by reclamation: 0.007295 seconds Time taken by reclamation: 0.007731 seconds Time taken by reclamation: 0.007134 seconds Time taken by reclamation: 0.007285 seconds Time taken by reclamation: 0.007720 seconds Time taken by reclamation: 0.007128 seconds Time taken by reclamation: 0.007710 seconds Time taken by reclamation: 0.007712 seconds Time taken by reclamation: 0.007236 seconds Time taken by reclamation: 0.007690 seconds Time taken by reclamation: 0.007174 seconds Time taken by reclamation: 0.007670 seconds Time taken by reclamation: 0.007169 seconds Time taken by reclamation: 0.007305 seconds Time taken by reclamation: 0.007432 seconds Time taken by reclamation: 0.007158 seconds Time taken by reclamation: 0.007133 seconds =E2=80=A6 w/ patch ~ # ./a.out Time taken by reclamation: 0.002124 seconds Time taken by reclamation: 0.002116 seconds Time taken by reclamation: 0.002150 seconds Time taken by reclamation: 0.002261 seconds Time taken by reclamation: 0.002137 seconds Time taken by reclamation: 0.002173 seconds Time taken by reclamation: 0.002063 seconds Time taken by reclamation: 0.002088 seconds Time taken by reclamation: 0.002169 seconds Time taken by reclamation: 0.002124 seconds Time taken by reclamation: 0.002111 seconds Time taken by reclamation: 0.002224 seconds Time taken by reclamation: 0.002297 seconds Time taken by reclamation: 0.002260 seconds Time taken by reclamation: 0.002246 seconds Time taken by reclamation: 0.002272 seconds Time taken by reclamation: 0.002277 seconds Time taken by reclamation: 0.002462 seconds =E2=80=A6 This patch significantly speeds up try_to_unmap_one() by allowing it to skip redirtied THPs without splitting the PMD. Suggested-by: Baolin Wang Suggested-by: Lance Yang Signed-off-by: Barry Song Reviewed-by: Baolin Wang Reviewed-by: Lance Yang --- mm/huge_memory.c | 24 +++++++++++++++++------- mm/rmap.c | 13 ++++++++++--- 2 files changed, 27 insertions(+), 10 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 2eda2a9ec8fc..ab80348f33dd 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3176,8 +3176,12 @@ static bool __discard_anon_folio_pmd_locked(struct v= m_area_struct *vma, int ref_count, map_count; pmd_t orig_pmd =3D *pmdp; =20 - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) + if (pmd_dirty(orig_pmd)) + folio_set_dirty(folio); + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { + folio_set_swapbacked(folio); return false; + } =20 orig_pmd =3D pmdp_huge_clear_flush(vma, addr, pmdp); =20 @@ -3204,8 +3208,15 @@ static bool __discard_anon_folio_pmd_locked(struct v= m_area_struct *vma, * * The only folio refs must be one from isolation plus the rmap(s). */ - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) || - ref_count !=3D map_count + 1) { + if (pmd_dirty(orig_pmd)) + folio_set_dirty(folio); + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { + folio_set_swapbacked(folio); + set_pmd_at(mm, addr, pmdp, orig_pmd); + return false; + } + + if (ref_count !=3D map_count + 1) { set_pmd_at(mm, addr, pmdp, orig_pmd); return false; } @@ -3225,12 +3236,11 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *v= ma, unsigned long addr, { VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio); VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); + VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio); VM_WARN_ON_ONCE(!IS_ALIGNED(addr, HPAGE_PMD_SIZE)); =20 - if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) - return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); - - return false; + return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); } =20 static void remap_page(struct folio *folio, unsigned long nr, int flags) diff --git a/mm/rmap.c b/mm/rmap.c index 8786704bd466..bcec8677f68d 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1863,9 +1863,16 @@ static bool try_to_unmap_one(struct folio *folio, st= ruct vm_area_struct *vma, } =20 if (!pvmw.pte) { - if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, - folio)) - goto walk_done; + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) { + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio)) + goto walk_done; + /* + * unmap_huge_pmd_locked has either already marked + * the folio as swap-backed or decided to retain it + * due to GUP or speculative references. + */ + goto walk_abort; + } =20 if (flags & TTU_SPLIT_HUGE_PMD) { /* --=20 2.39.3 (Apple Git-146)