From nobody Sun Feb 8 14:53:17 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 3D2AAC001B0 for ; Wed, 19 Jul 2023 13:55:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230447AbjGSNzL (ORCPT ); Wed, 19 Jul 2023 09:55:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37010 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230020AbjGSNzH (ORCPT ); Wed, 19 Jul 2023 09:55:07 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 64BC312C for ; Wed, 19 Jul 2023 06:55:06 -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 6CEF3D75; Wed, 19 Jul 2023 06:55:49 -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 90B6C3F6C4; Wed, 19 Jul 2023 06:55:04 -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 v2 1/3] mm: Allow deferred splitting of arbitrary large anon folios Date: Wed, 19 Jul 2023 14:54:48 +0100 Message-Id: <20230719135450.545227-2-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230719135450.545227-1-ryan.roberts@arm.com> References: <20230719135450.545227-1-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 Sun Feb 8 14:53:17 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 5B4BAEB64DA for ; Wed, 19 Jul 2023 13:55:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230135AbjGSNzO (ORCPT ); Wed, 19 Jul 2023 09:55:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229539AbjGSNzJ (ORCPT ); Wed, 19 Jul 2023 09:55:09 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3F0B112C for ; Wed, 19 Jul 2023 06:55:08 -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 4238512FC; Wed, 19 Jul 2023 06:55:51 -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 672B43F6C4; Wed, 19 Jul 2023 06:55:06 -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 v2 2/3] mm: Implement folio_remove_rmap_range() Date: Wed, 19 Jul 2023 14:54:49 +0100 Message-Id: <20230719135450.545227-3-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230719135450.545227-1-ryan.roberts@arm.com> References: <20230719135450.545227-1-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. Reviewed-by: Yin Fengwei Reviewed-by: Zi Yan Signed-off-by: Ryan Roberts --- include/linux/rmap.h | 2 ++ mm/rmap.c | 72 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 74 insertions(+) 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..4022a3ab73a8 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1359,6 +1359,78 @@ void page_add_file_rmap(struct page *page, struct vm= _area_struct *vma, mlock_vma_folio(folio, vma, compound); } =20 +/** + * 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; + bool last; + enum node_stat_item idx; + + 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; + } + + if (nr_unmapped) { + idx =3D folio_test_anon(folio) ? NR_ANON_MAPPED : NR_FILE_MAPPED; + __lruvec_stat_mod_folio(folio, idx, -nr_unmapped); + + /* + * 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) && 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, false); +} + /** * page_remove_rmap - take down pte mapping from a page * @page: page to remove mapping from --=20 2.25.1 From nobody Sun Feb 8 14:53:17 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 D0B8DC0015E for ; Wed, 19 Jul 2023 13:55:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231439AbjGSNzY (ORCPT ); Wed, 19 Jul 2023 09:55:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37066 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231345AbjGSNzS (ORCPT ); Wed, 19 Jul 2023 09:55:18 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 13A551998 for ; Wed, 19 Jul 2023 06:55:15 -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 1A0532F4; Wed, 19 Jul 2023 06:55:58 -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 3DE203F6C4; Wed, 19 Jul 2023 06:55:08 -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 v2 3/3] mm: Batch-zap large anonymous folio PTE mappings Date: Wed, 19 Jul 2023 14:54:50 +0100 Message-Id: <20230719135450.545227-4-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230719135450.545227-1-ryan.roberts@arm.com> References: <20230719135450.545227-1-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