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Rao" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , "David S. Miller" , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org Subject: [PATCH v1 09/11] mm/memory: optimize fork() with PTE-mapped THP Date: Mon, 22 Jan 2024 20:41:58 +0100 Message-ID: <20240122194200.381241-10-david@redhat.com> In-Reply-To: <20240122194200.381241-1-david@redhat.com> References: <20240122194200.381241-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.1 X-Rspamd-Queue-Id: CE74F1C0005 X-Rspam-User: X-Stat-Signature: zsddtotsfcn9gcpyuu3dwr3nua8ngbjh X-Rspamd-Server: rspam01 X-HE-Tag: 1705952585-279268 X-HE-Meta: U2FsdGVkX1+kPijHCDb9kpDzOrbQsNOF1rAOkERGR6tyApKiHmtcsiRn4q6uiBQq48W/TyKM495P9BtjensWtYxSXv5DF4Z1MQDZxIyUZgvyH3t5weAWOgiBk5zUmoRZuy7rgIxbgDpwXUpC5Tu+B+Zesb7fOYqB+L88cbLwOovfmP1lydti2wS3X386yPQQ+1uYfemmiksV/RtQtWHur51icWdq9L8Wf5qZeLnbBAV+6B0CzvgzaDhuHDcZfQfZ0vZDz24N7j8IBs354U2g0zfl+5KbTuzoy7QF3maTrO6fBxg3nCQ5RpMT+h3Q8WyqV0sJWAtxGS4g2FDaUMDYlgojs3qUBnJP733o+HLm2/8JGk4Exg19cmKvY6LJho5bzm/svPQB2o0tKpvb3DLx0gFUh/znpv7TagC5nIaDxnj5pLA5+QIJp582ZxpmSK8y48NUUDgfS7Z/dP1w8TDmMnFura2952fQEUmp1Y3rFYSuELGNDQmqHXVq514IJEHFJ+rgBu5TShOz3qfMAx+yVtK1R5uwaEv9QbM0WteiVhd12wHzJOEm2ilyxPUqncVlfzvUevyvDIEK+dc5GmzMEji7A/+UCUSKigWJXbH97hm0+tPvFOF0kkypCUvdYz4xqKmDS/1Vp+tWpnolvOLFgji5yaw8lOqmWSfg1wkI3ofhcihGTMKbrsGYkT13WFWr/6YrdJhZD0hmcdOd5BGGB50O5/AHMV1HSNOdF5OOdu7mHAF2ZEMacKBMZGQqa9Ob64GD4J6mv4zTAi1t2SQETgsu0kaDshIYVN2o0jN1I8dlD5MeZDCRw6OejNljjmfz2qmG2JnZKJzEzwaozU85BrdSc2zAT9PLq53yjCNuZwGSS6skHVmnv4So8xOdTTWjolFXavUcKeyLxdX5SsBVx/8YL+X2Lx0/r/klOw7XzIf2/1IiHiOzqW5g6jAVImn8fmOLpw9IbBxB0uFEzzO ukVU9MPY 7TAOWlq6wjHv/LddN3zw5bW15/FI84ikJBjj/9ESOlV0JBKQIx2WxvACNgWs/d+VUFR89Mzi4UpCLKbdyzgbVE4eQRxVhvOH0YKREgGTPMaSP6CivEofNf1oxz8P0rImi8iOvx7ZTwtMBu51R+3GhFJj1d5ktERPmu3SGirgfJ7mTSLQ= 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: Let's implement PTE batching when consecutive (present) PTEs map consecutive pages of the same large folio, and all other PTE bits besides the PFNs are equal. We will optimize folio_pte_batch() separately, to ignore some other PTE bits. This patch is based on work by Ryan Roberts. Use __always_inline for __copy_present_ptes() and keep the handling for single PTEs completely separate from the multi-PTE case: we really want the compiler to optimize for the single-PTE case with small folios, to not degrade performance. Note that PTE batching will never exceed a single page table and will always stay within VMA boundaries. Signed-off-by: David Hildenbrand --- include/linux/pgtable.h | 17 +++++- mm/memory.c | 113 +++++++++++++++++++++++++++++++++------- 2 files changed, 109 insertions(+), 21 deletions(-) diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index f6d0e3513948a..d32cedf6936ba 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -212,8 +212,6 @@ static inline int pmd_dirty(pmd_t pmd) #define arch_flush_lazy_mmu_mode() do {} while (0) #endif -#ifndef set_ptes - #ifndef pte_next_pfn static inline pte_t pte_next_pfn(pte_t pte) { @@ -221,6 +219,7 @@ static inline pte_t pte_next_pfn(pte_t pte) } #endif +#ifndef set_ptes /** * set_ptes - Map consecutive pages to a contiguous range of addresses. * @mm: Address space to map the pages into. @@ -650,6 +649,20 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres } #endif +#ifndef wrprotect_ptes +static inline void wrprotect_ptes(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, unsigned int nr) +{ + for (;;) { + ptep_set_wrprotect(mm, addr, ptep); + if (--nr == 0) + break; + ptep++; + addr += PAGE_SIZE; + } +} +#endif + /* * On some architectures hardware does not set page access bit when accessing * memory page, it is responsibility of software setting this bit. It brings diff --git a/mm/memory.c b/mm/memory.c index 185b4aff13d62..f563aec85b2a8 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -930,15 +930,15 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma return 0; } -static inline void __copy_present_pte(struct vm_area_struct *dst_vma, +static __always_inline void __copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, pte_t *dst_pte, pte_t *src_pte, - pte_t pte, unsigned long addr) + pte_t pte, unsigned long addr, int nr) { struct mm_struct *src_mm = src_vma->vm_mm; /* If it's a COW mapping, write protect it both processes. */ if (is_cow_mapping(src_vma->vm_flags) && pte_write(pte)) { - ptep_set_wrprotect(src_mm, addr, src_pte); + wrprotect_ptes(src_mm, addr, src_pte, nr); pte = pte_wrprotect(pte); } @@ -950,26 +950,94 @@ static inline void __copy_present_pte(struct vm_area_struct *dst_vma, if (!userfaultfd_wp(dst_vma)) pte = pte_clear_uffd_wp(pte); - set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte); + set_ptes(dst_vma->vm_mm, addr, dst_pte, pte, nr); +} + +/* + * Detect a PTE batch: consecutive (present) PTEs that map consecutive + * pages of the same folio. + * + * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN. + */ +static inline int folio_pte_batch(struct folio *folio, unsigned long addr, + pte_t *start_ptep, pte_t pte, int max_nr) +{ + unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio); + const pte_t *end_ptep = start_ptep + max_nr; + pte_t expected_pte = pte_next_pfn(pte); + pte_t *ptep = start_ptep + 1; + + VM_WARN_ON_FOLIO(!pte_present(pte), folio); + + while (ptep != end_ptep) { + pte = ptep_get(ptep); + + if (!pte_same(pte, expected_pte)) + break; + + /* + * Stop immediately once we reached the end of the folio. In + * corner cases the next PFN might fall into a different + * folio. + */ + if (pte_pfn(pte) == folio_end_pfn) + break; + + expected_pte = pte_next_pfn(expected_pte); + ptep++; + } + + return ptep - start_ptep; } /* - * Copy one pte. Returns 0 if succeeded, or -EAGAIN if one preallocated page - * is required to copy this pte. + * Copy one present PTE, trying to batch-process subsequent PTEs that map + * consecutive pages of the same folio by copying them as well. + * + * Returns -EAGAIN if one preallocated page is required to copy the next PTE. + * Otherwise, returns the number of copied PTEs (at least 1). */ static inline int -copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, +copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, pte_t *dst_pte, pte_t *src_pte, pte_t pte, unsigned long addr, - int *rss, struct folio **prealloc) + int max_nr, int *rss, struct folio **prealloc) { struct page *page; struct folio *folio; + int err, nr; page = vm_normal_page(src_vma, addr, pte); if (unlikely(!page)) goto copy_pte; folio = page_folio(page); + + /* + * If we likely have to copy, just don't bother with batching. Make + * sure that the common "small folio" case stays as fast as possible + * by keeping the batching logic separate. + */ + if (unlikely(!*prealloc && folio_test_large(folio) && max_nr != 1)) { + nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr); + if (folio_test_anon(folio)) { + folio_ref_add(folio, nr); + if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page, + nr, src_vma))) { + folio_ref_sub(folio, nr); + return -EAGAIN; + } + rss[MM_ANONPAGES] += nr; + VM_WARN_ON_FOLIO(PageAnonExclusive(page), folio); + } else { + folio_ref_add(folio, nr); + folio_dup_file_rmap_ptes(folio, page, nr); + rss[mm_counter_file(page)] += nr; + } + __copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte, + addr, nr); + return nr; + } + if (folio_test_anon(folio)) { /* * If this page may have been pinned by the parent process, @@ -981,8 +1049,9 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, if (unlikely(folio_try_dup_anon_rmap_pte(folio, page, src_vma))) { /* Page may be pinned, we have to copy. */ folio_put(folio); - return copy_present_page(dst_vma, src_vma, dst_pte, src_pte, - addr, rss, prealloc, page); + err = copy_present_page(dst_vma, src_vma, dst_pte, src_pte, + addr, rss, prealloc, page); + return err ? err : 1; } rss[MM_ANONPAGES]++; VM_WARN_ON_FOLIO(PageAnonExclusive(page), folio); @@ -993,8 +1062,8 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, } copy_pte: - __copy_present_pte(dst_vma, src_vma, dst_pte, src_pte, pte, addr); - return 0; + __copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte, addr, 1); + return 1; } static inline struct folio *folio_prealloc(struct mm_struct *src_mm, @@ -1031,10 +1100,11 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, pte_t *src_pte, *dst_pte; pte_t ptent; spinlock_t *src_ptl, *dst_ptl; - int progress, ret = 0; + int progress, max_nr, ret = 0; int rss[NR_MM_COUNTERS]; swp_entry_t entry = (swp_entry_t){0}; struct folio *prealloc = NULL; + int nr; again: progress = 0; @@ -1065,6 +1135,8 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, arch_enter_lazy_mmu_mode(); do { + nr = 1; + /* * We are holding two locks at this point - either of them * could generate latencies in another task on another CPU. @@ -1101,9 +1173,10 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, */ WARN_ON_ONCE(ret != -ENOENT); } - /* copy_present_pte() will clear `*prealloc' if consumed */ - ret = copy_present_pte(dst_vma, src_vma, dst_pte, src_pte, - ptent, addr, rss, &prealloc); + /* copy_present_ptes() will clear `*prealloc' if consumed */ + max_nr = (end - addr) / PAGE_SIZE; + ret = copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, + ptent, addr, max_nr, rss, &prealloc); /* * If we need a pre-allocated page for this pte, drop the * locks, allocate, and try again. @@ -1120,8 +1193,10 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, folio_put(prealloc); prealloc = NULL; } - progress += 8; - } while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end); + nr = ret; + progress += 8 * nr; + } while (dst_pte += nr, src_pte += nr, addr += PAGE_SIZE * nr, + addr != end); arch_leave_lazy_mmu_mode(); pte_unmap_unlock(orig_src_pte, src_ptl); @@ -1142,7 +1217,7 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, prealloc = folio_prealloc(src_mm, src_vma, addr, false); if (!prealloc) return -ENOMEM; - } else if (ret) { + } else if (ret < 0) { VM_WARN_ON_ONCE(1); }