From nobody Mon Feb 9 05:53:00 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E38EBEB64DC for ; Thu, 20 Jul 2023 11:30:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231345AbjGTLaM (ORCPT ); Thu, 20 Jul 2023 07:30:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37064 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231338AbjGTLaL (ORCPT ); Thu, 20 Jul 2023 07:30:11 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 816F4B7 for ; Thu, 20 Jul 2023 04:30:10 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8F7172F4; Thu, 20 Jul 2023 04:30:53 -0700 (PDT) Received: from e125769.cambridge.arm.com (e125769.cambridge.arm.com [10.1.196.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AD2953F6C4; Thu, 20 Jul 2023 04:30:08 -0700 (PDT) From: Ryan Roberts To: Andrew Morton , Matthew Wilcox , Yin Fengwei , David Hildenbrand , Yu Zhao , Yang Shi , "Huang, Ying" , Zi Yan Cc: Ryan Roberts , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 1/3] mm: Allow deferred splitting of arbitrary large anon folios Date: Thu, 20 Jul 2023 12:29:53 +0100 Message-Id: <20230720112955.643283-2-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230720112955.643283-1-ryan.roberts@arm.com> References: <20230720112955.643283-1-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" In preparation for the introduction of large folios for anonymous memory, we would like to be able to split them when they have unmapped subpages, in order to free those unused pages under memory pressure. So remove the artificial requirement that the large folio needed to be at least PMD-sized. Reviewed-by: Yu Zhao Reviewed-by: Yin Fengwei Reviewed-by: Matthew Wilcox (Oracle) Reviewed-by: David Hildenbrand Signed-off-by: Ryan Roberts --- mm/rmap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index 0c0d8857dfce..eb0bb00dae34 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1426,11 +1426,11 @@ void page_remove_rmap(struct page *page, struct vm_= area_struct *vma, __lruvec_stat_mod_folio(folio, idx, -nr); =20 /* - * Queue anon THP for deferred split if at least one + * Queue anon large folio for deferred split if at least one * page of the folio is unmapped and at least one page * is still mapped. */ - if (folio_test_pmd_mappable(folio) && folio_test_anon(folio)) + if (folio_test_large(folio) && folio_test_anon(folio)) if (!compound || nr < nr_pmdmapped) deferred_split_folio(folio); } --=20 2.25.1 From nobody Mon Feb 9 05:53:00 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C400BC001DC for ; Thu, 20 Jul 2023 11:30:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231391AbjGTLaP (ORCPT ); Thu, 20 Jul 2023 07:30:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37078 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231338AbjGTLaN (ORCPT ); Thu, 20 Jul 2023 07:30:13 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 52F29BB for ; Thu, 20 Jul 2023 04:30:12 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 65F80D75; Thu, 20 Jul 2023 04:30:55 -0700 (PDT) Received: from e125769.cambridge.arm.com (e125769.cambridge.arm.com [10.1.196.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 83B843F6C4; Thu, 20 Jul 2023 04:30:10 -0700 (PDT) From: Ryan Roberts To: Andrew Morton , Matthew Wilcox , Yin Fengwei , David Hildenbrand , Yu Zhao , Yang Shi , "Huang, Ying" , Zi Yan Cc: Ryan Roberts , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 2/3] mm: Implement folio_remove_rmap_range() Date: Thu, 20 Jul 2023 12:29:54 +0100 Message-Id: <20230720112955.643283-3-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230720112955.643283-1-ryan.roberts@arm.com> References: <20230720112955.643283-1-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Like page_remove_rmap() but batch-removes the rmap for a range of pages belonging to a folio. This can provide a small speedup due to less manipuation of the various counters. But more crucially, if removing the rmap for all pages of a folio in a batch, there is no need to (spuriously) add it to the deferred split list, which saves significant cost when there is contention for the split queue lock. All contained pages are accounted using the order-0 folio (or base page) scheme. page_remove_rmap() is refactored so that it forwards to folio_remove_rmap_range() for !compound cases, and both functions now share a common epilogue function. The intention here is to avoid duplication of code. Signed-off-by: Ryan Roberts --- include/linux/rmap.h | 2 + mm/rmap.c | 125 ++++++++++++++++++++++++++++++++----------- 2 files changed, 97 insertions(+), 30 deletions(-) diff --git a/include/linux/rmap.h b/include/linux/rmap.h index b87d01660412..f578975c12c0 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -200,6 +200,8 @@ void page_add_file_rmap(struct page *, struct vm_area_s= truct *, bool compound); void page_remove_rmap(struct page *, struct vm_area_struct *, bool compound); +void folio_remove_rmap_range(struct folio *folio, struct page *page, + int nr, struct vm_area_struct *vma); =20 void hugepage_add_anon_rmap(struct page *, struct vm_area_struct *, unsigned long address, rmap_t flags); diff --git a/mm/rmap.c b/mm/rmap.c index eb0bb00dae34..c3ef56f7ec15 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1359,6 +1359,94 @@ void page_add_file_rmap(struct page *page, struct vm= _area_struct *vma, mlock_vma_folio(folio, vma, compound); } =20 +/** + * __remove_rmap_finish - common operations when taking down a mapping. + * @folio: Folio containing all pages taken down. + * @vma: The VM area containing the range. + * @compound: True if pages were taken down from PMD or false if from PTE(= s). + * @nr_unmapped: Number of pages within folio that are now unmapped. + * @nr_mapped: Number of pages within folio that are still mapped. + */ +static void __remove_rmap_finish(struct folio *folio, + struct vm_area_struct *vma, bool compound, + int nr_unmapped, int nr_mapped) +{ + enum node_stat_item idx; + + if (nr_unmapped) { + idx =3D folio_test_anon(folio) ? NR_ANON_MAPPED : NR_FILE_MAPPED; + __lruvec_stat_mod_folio(folio, idx, -nr_unmapped); + + /* + * Queue large anon folio for deferred split if at least one + * page of the folio is unmapped and at least one page is still + * mapped. + */ + if (folio_test_large(folio) && + folio_test_anon(folio) && nr_mapped) + deferred_split_folio(folio); + } + + /* + * It would be tidy to reset folio_test_anon mapping when fully + * unmapped, but that might overwrite a racing page_add_anon_rmap + * which increments mapcount after us but sets mapping before us: + * so leave the reset to free_pages_prepare, and remember that + * it's only reliable while mapped. + */ + + munlock_vma_folio(folio, vma, compound); +} + +/** + * folio_remove_rmap_range - Take down PTE mappings from a range of pages. + * @folio: Folio containing all pages in range. + * @page: First page in range to unmap. + * @nr: Number of pages to unmap. + * @vma: The VM area containing the range. + * + * All pages in the range must belong to the same VMA & folio. They must be + * mapped with PTEs, not a PMD. + * + * Context: Caller holds the pte lock. + */ +void folio_remove_rmap_range(struct folio *folio, struct page *page, + int nr, struct vm_area_struct *vma) +{ + atomic_t *mapped =3D &folio->_nr_pages_mapped; + int nr_unmapped =3D 0; + int nr_mapped =3D 0; + bool last; + + if (unlikely(folio_test_hugetlb(folio))) { + VM_WARN_ON_FOLIO(1, folio); + return; + } + + VM_WARN_ON_ONCE(page < &folio->page || + page + nr > (&folio->page + folio_nr_pages(folio))); + + if (!folio_test_large(folio)) { + /* Is this the page's last map to be removed? */ + last =3D atomic_add_negative(-1, &page->_mapcount); + nr_unmapped =3D last; + } else { + for (; nr !=3D 0; nr--, page++) { + /* Is this the page's last map to be removed? */ + last =3D atomic_add_negative(-1, &page->_mapcount); + if (last) + nr_unmapped++; + } + + /* Pages still mapped if folio mapped entirely */ + nr_mapped =3D atomic_sub_return_relaxed(nr_unmapped, mapped); + if (nr_mapped >=3D COMPOUND_MAPPED) + nr_unmapped =3D 0; + } + + __remove_rmap_finish(folio, vma, false, nr_unmapped, nr_mapped); +} + /** * page_remove_rmap - take down pte mapping from a page * @page: page to remove mapping from @@ -1385,15 +1473,13 @@ void page_remove_rmap(struct page *page, struct vm_= area_struct *vma, return; } =20 - /* Is page being unmapped by PTE? Is this its last map to be removed? */ + /* Is page being unmapped by PTE? */ if (likely(!compound)) { - last =3D atomic_add_negative(-1, &page->_mapcount); - nr =3D last; - if (last && folio_test_large(folio)) { - nr =3D atomic_dec_return_relaxed(mapped); - nr =3D (nr < COMPOUND_MAPPED); - } - } else if (folio_test_pmd_mappable(folio)) { + folio_remove_rmap_range(folio, page, 1, vma); + return; + } + + if (folio_test_pmd_mappable(folio)) { /* That test is redundant: it's for safety or to optimize out */ =20 last =3D atomic_add_negative(-1, &folio->_entire_mapcount); @@ -1421,29 +1507,8 @@ void page_remove_rmap(struct page *page, struct vm_a= rea_struct *vma, idx =3D NR_FILE_PMDMAPPED; __lruvec_stat_mod_folio(folio, idx, -nr_pmdmapped); } - if (nr) { - idx =3D folio_test_anon(folio) ? NR_ANON_MAPPED : NR_FILE_MAPPED; - __lruvec_stat_mod_folio(folio, idx, -nr); - - /* - * Queue anon large folio for deferred split if at least one - * page of the folio is unmapped and at least one page - * is still mapped. - */ - if (folio_test_large(folio) && folio_test_anon(folio)) - if (!compound || nr < nr_pmdmapped) - deferred_split_folio(folio); - } - - /* - * It would be tidy to reset folio_test_anon mapping when fully - * unmapped, but that might overwrite a racing page_add_anon_rmap - * which increments mapcount after us but sets mapping before us: - * so leave the reset to free_pages_prepare, and remember that - * it's only reliable while mapped. - */ =20 - munlock_vma_folio(folio, vma, compound); + __remove_rmap_finish(folio, vma, compound, nr, nr_pmdmapped - nr); } =20 /* --=20 2.25.1 From nobody Mon Feb 9 05:53:00 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CEA6FEB64DA for ; Thu, 20 Jul 2023 11:30:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231440AbjGTLaS (ORCPT ); Thu, 20 Jul 2023 07:30:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37116 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231409AbjGTLaP (ORCPT ); Thu, 20 Jul 2023 07:30:15 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 32489123 for ; Thu, 20 Jul 2023 04:30:14 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3C758139F; Thu, 20 Jul 2023 04:30:57 -0700 (PDT) Received: from e125769.cambridge.arm.com (e125769.cambridge.arm.com [10.1.196.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5A2CA3F6C4; Thu, 20 Jul 2023 04:30:12 -0700 (PDT) From: Ryan Roberts To: Andrew Morton , Matthew Wilcox , Yin Fengwei , David Hildenbrand , Yu Zhao , Yang Shi , "Huang, Ying" , Zi Yan Cc: Ryan Roberts , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 3/3] mm: Batch-zap large anonymous folio PTE mappings Date: Thu, 20 Jul 2023 12:29:55 +0100 Message-Id: <20230720112955.643283-4-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230720112955.643283-1-ryan.roberts@arm.com> References: <20230720112955.643283-1-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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. Signed-off-by: Ryan Roberts --- mm/memory.c | 120 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 120 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index 01f39e8144ef..189b1cfd823d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1391,6 +1391,94 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct = *vma, pte_install_uffd_wp_if_needed(vma, addr, pte, pteval); } =20 +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 =3D (page_to_pfn(page) - page_to_pfn(anchor)) << PAGE_SHIFT; + vaddr =3D 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 =3D &folio->page + folio_nr_pages(folio); + end =3D min(page_cont_mapped_vaddr(folio_end, page, addr), end); + floops =3D (end - addr) >> PAGE_SHIFT; + pfn =3D page_to_pfn(page); + pfn++; + pte++; + + for (i =3D 1; i < floops; i++) { + ptent =3D ptep_get(pte); + + if (!pte_present(ptent) || pte_pfn(ptent) !=3D 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 =3D tlb->mm; + pte_t ptent; + bool full; + int i; + + for (i =3D 0; i < nr_pages;) { + ptent =3D 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 =3D __tlb_remove_page(tlb, page, 0); + + if (unlikely(page_mapcount(page) < 1)) + print_bad_pte(vma, addr, ptent, page); + + i++; + page++; + pte++; + addr +=3D PAGE_SIZE; + + if (unlikely(full)) + break; + } + + folio_remove_rmap_range(folio, page - i, i, vma); + + 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 +1516,38 @@ static unsigned long zap_pte_range(struct mmu_gather= *tlb, page =3D 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 =3D page_folio(page); + int nr_pages_req, nr_pages; + + nr_pages_req =3D folio_nr_pages_cont_mapped( + folio, page, pte, addr, end); + + nr_pages =3D try_zap_anon_pte_range(tlb, vma, + folio, page, pte, addr, + nr_pages_req, details); + + rss[mm_counter(page)] -=3D nr_pages; + nr_pages--; + pte +=3D nr_pages; + addr +=3D nr_pages << PAGE_SHIFT; + + if (unlikely(nr_pages < nr_pages_req)) { + force_flush =3D 1; + addr +=3D PAGE_SIZE; + break; + } + continue; + } + ptent =3D ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm); tlb_remove_tlb_entry(tlb, pte, addr); --=20 2.25.1