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Thu, 27 Jul 2023 07:18:53 -0700 (PDT) From: Ryan Roberts To: Andrew Morton , Matthew Wilcox , Yin Fengwei , David Hildenbrand , Yu Zhao , Yang Shi , "Huang, Ying" , Zi Yan , Nathan Chancellor , Alexander Gordeev , Gerald Schaefer Cc: Ryan Roberts , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v4 3/3] mm: Batch-zap large anonymous folio PTE mappings Date: Thu, 27 Jul 2023 15:18:37 +0100 Message-Id: <20230727141837.3386072-4-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230727141837.3386072-1-ryan.roberts@arm.com> References: <20230727141837.3386072-1-ryan.roberts@arm.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: D1D4014000D X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 4wuktwd463srfjxe4a77eqqgjfufumg7 X-HE-Tag: 1690467536-556317 X-HE-Meta: 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 kS1UWyPJ B3LQJtghWeNoOc0IPK3+H98xQYM4SrdmKkY3B+gPP6qkJEPwbFxEPSxOZtGCDFJd45g37qePv/sozlWcgbSo6JLICoMQdEtsTyL6DkOxR0Ad5gQZZVXt7Mma1zDTmMdjAKF7WcczxwpQ39AsrquZMsgC/t2xFiImH2vSU 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: This allows batching the rmap removal with folio_remove_rmap_range(), which means we avoid spuriously adding a partially unmapped folio to the deferred split queue in the common case, which reduces split queue lock contention. Previously each page was removed from the rmap individually with page_remove_rmap(). If the first page belonged to a large folio, this would cause page_remove_rmap() to conclude that the folio was now partially mapped and add the folio to the deferred split queue. But subsequent calls would cause the folio to become fully unmapped, meaning there is no value to adding it to the split queue. A complicating factor is that for platforms where MMU_GATHER_NO_GATHER is enabled (e.g. s390), __tlb_remove_page() drops a reference to the page. This means that the folio reference count could drop to zero while still in use (i.e. before folio_remove_rmap_range() is called). This does not happen on other platforms because the actual page freeing is deferred. Solve this by appropriately getting/putting the folio to guarrantee it does not get freed early. Given the need to get/put the folio in the batch path, we stick to the non-batched path if the folio is not large. While the batched path is functionally correct for a folio with 1 page, it is unlikely to be as efficient as the existing non-batched path in this case. Signed-off-by: Ryan Roberts --- mm/memory.c | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 132 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index 01f39e8144ef..d35bd8d2b855 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1391,6 +1391,99 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct *vma, pte_install_uffd_wp_if_needed(vma, addr, pte, pteval); } +static inline unsigned long page_cont_mapped_vaddr(struct page *page, + struct page *anchor, unsigned long anchor_vaddr) +{ + unsigned long offset; + unsigned long vaddr; + + offset = (page_to_pfn(page) - page_to_pfn(anchor)) << PAGE_SHIFT; + vaddr = anchor_vaddr + offset; + + if (anchor > page) { + if (vaddr > anchor_vaddr) + return 0; + } else { + if (vaddr < anchor_vaddr) + return ULONG_MAX; + } + + return vaddr; +} + +static int folio_nr_pages_cont_mapped(struct folio *folio, + struct page *page, pte_t *pte, + unsigned long addr, unsigned long end) +{ + pte_t ptent; + int floops; + int i; + unsigned long pfn; + struct page *folio_end; + + if (!folio_test_large(folio)) + return 1; + + folio_end = &folio->page + folio_nr_pages(folio); + end = min(page_cont_mapped_vaddr(folio_end, page, addr), end); + floops = (end - addr) >> PAGE_SHIFT; + pfn = page_to_pfn(page); + pfn++; + pte++; + + for (i = 1; i < floops; i++) { + ptent = ptep_get(pte); + + if (!pte_present(ptent) || pte_pfn(ptent) != pfn) + break; + + pfn++; + pte++; + } + + return i; +} + +static unsigned long try_zap_anon_pte_range(struct mmu_gather *tlb, + struct vm_area_struct *vma, + struct folio *folio, + struct page *page, pte_t *pte, + unsigned long addr, int nr_pages, + struct zap_details *details) +{ + struct mm_struct *mm = tlb->mm; + pte_t ptent; + bool full; + int i; + + /* __tlb_remove_page may drop a ref; prevent going to 0 while in use. */ + folio_get(folio); + + for (i = 0; i < nr_pages;) { + ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm); + tlb_remove_tlb_entry(tlb, pte, addr); + zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent); + full = __tlb_remove_page(tlb, page, 0); + + if (unlikely(page_mapcount(page) < 1)) + print_bad_pte(vma, addr, ptent, page); + + i++; + page++; + pte++; + addr += PAGE_SIZE; + + if (unlikely(full)) + break; + } + + folio_remove_rmap_range(folio, page - i, i, vma); + + folio_put(folio); + + return i; +} + static unsigned long zap_pte_range(struct mmu_gather *tlb, struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr, unsigned long end, @@ -1428,6 +1521,45 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, page = vm_normal_page(vma, addr, ptent); if (unlikely(!should_zap_page(details, page))) continue; + + /* + * Batch zap large anonymous folio mappings. This allows + * batching the rmap removal, which means we avoid + * spuriously adding a partially unmapped folio to the + * deferrred split queue in the common case, which + * reduces split queue lock contention. + */ + if (page && PageAnon(page)) { + struct folio *folio = page_folio(page); + + if (folio_test_large(folio)) { + int nr_pages_req, nr_pages; + int counter = mm_counter(page); + + nr_pages_req = folio_nr_pages_cont_mapped( + folio, page, pte, addr, + end); + + /* folio may be freed on return. */ + nr_pages = try_zap_anon_pte_range( + tlb, vma, folio, page, + pte, addr, nr_pages_req, + details); + + rss[counter] -= nr_pages; + nr_pages--; + pte += nr_pages; + addr += nr_pages << PAGE_SHIFT; + + if (unlikely(nr_pages < nr_pages_req)) { + force_flush = 1; + addr += PAGE_SIZE; + break; + } + continue; + } + } + ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm); tlb_remove_tlb_entry(tlb, pte, addr);