From nobody Sun Feb 8 04:34:10 2026 Received: from out30-111.freemail.mail.aliyun.com (out30-111.freemail.mail.aliyun.com [115.124.30.111]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E508D25393E for ; Tue, 23 Dec 2025 05:54:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.111 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766469254; cv=none; b=rcgj7LQhhZ12JgqiC1CKQabB5CogRNuhYrQHp+AQWw6Y8oUOIpD0l08vEfy9WCuO+Qj6cT/JUgV6sc79ffQ/+i1WmhH1/baPre85wC4sJgEjEi2DjBkJZ0oO5MRkW68ALp7VFN03E7FUaEen+D2DbDMeh16eX4YD2R+GiLOeTqs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766469254; c=relaxed/simple; bh=mPyX/3tsCchvnKZZmrzfwqNAy3u7q97O4neROMVe1a0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hH+oLJIco1taSpc4jJlcPQ1G39t4pb0g9wP35Vonb8YRqVTJKkz5mouYYn3R6PEVn7Saw3p/2Ihjy6j0VGRWD0uACArNQQMfZWBCU0vepCAC9cJ+s2Rg4iNYqq+mMrdrtIdJY0EMpc9S/DXxxPhEwAgpfP0e3oTWa2jJurCaxx4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=d1TRrJC6; arc=none smtp.client-ip=115.124.30.111 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="d1TRrJC6" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1766469245; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=MSFx6Rnw8Uesz11I46fNYvPpzwOjE58x5E7aQ6mIcqg=; b=d1TRrJC61E5OYsw/mYuv3jyK6x1CIxVikRNGSDB2IT7+3YlV08Sr9kGUZGGGyIAPTX2cHcuua3r/R0f19w9vJeW19buwN718fytQdCRB83sM95SafS8k0Y07zL2jL7We4bWKJNelJ8wupQMmC5zsJTPYEOLJbPDIKVWPxJV3uBw= Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WvWSzFR_1766468925 cluster:ay36) by smtp.aliyun-inc.com; Tue, 23 Dec 2025 13:48:45 +0800 From: Baolin Wang To: akpm@linux-foundation.org, david@kernel.org, catalin.marinas@arm.com, will@kernel.org Cc: lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, willy@infradead.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 1/5] mm: rmap: support batched checks of the references for large folios Date: Tue, 23 Dec 2025 13:48:35 +0800 Message-ID: X-Mailer: git-send-email 2.43.7 In-Reply-To: References: 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" Currently, folio_referenced_one() always checks the young flag for each PTE sequentially, which is inefficient for large folios. This inefficiency is especially noticeable when reclaiming clean file-backed large folios, where folio_referenced() is observed as a significant performance hotspot. Moreover, on Arm64 architecture, which supports contiguous PTEs, there is a= lready an optimization to clear the young flags for PTEs within a contiguous range. However, this is not sufficient. We can extend this to perform batched oper= ations for the entire large folio (which might exceed the contiguous range: CONT_P= TE_SIZE). Introduce a new API: clear_flush_young_ptes() to facilitate batched checking of the young flags and flushing TLB entries, thereby improving performance during large folio reclamation. And it will be overridden by the architectu= re that implements a more efficient batch operation in the following patches. Signed-off-by: Baolin Wang Reviewed-by: Ryan Roberts --- include/linux/mmu_notifier.h | 9 +++++---- include/linux/pgtable.h | 35 +++++++++++++++++++++++++++++++++++ mm/rmap.c | 29 +++++++++++++++++++++++++++-- 3 files changed, 67 insertions(+), 6 deletions(-) diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h index d1094c2d5fb6..dbbdcef4abf1 100644 --- a/include/linux/mmu_notifier.h +++ b/include/linux/mmu_notifier.h @@ -515,16 +515,17 @@ static inline void mmu_notifier_range_init_owner( range->owner =3D owner; } =20 -#define ptep_clear_flush_young_notify(__vma, __address, __ptep) \ +#define ptep_clear_flush_young_notify(__vma, __address, __ptep, __nr) \ ({ \ int __young; \ struct vm_area_struct *___vma =3D __vma; \ unsigned long ___address =3D __address; \ - __young =3D ptep_clear_flush_young(___vma, ___address, __ptep); \ + unsigned int ___nr =3D __nr; \ + __young =3D clear_flush_young_ptes(___vma, ___address, __ptep, ___nr); \ __young |=3D mmu_notifier_clear_flush_young(___vma->vm_mm, \ ___address, \ ___address + \ - PAGE_SIZE); \ + ___nr * PAGE_SIZE); \ __young; \ }) =20 @@ -650,7 +651,7 @@ static inline void mmu_notifier_subscriptions_destroy(s= truct mm_struct *mm) =20 #define mmu_notifier_range_update_to_read_only(r) false =20 -#define ptep_clear_flush_young_notify ptep_clear_flush_young +#define ptep_clear_flush_young_notify clear_flush_young_ptes #define pmdp_clear_flush_young_notify pmdp_clear_flush_young #define ptep_clear_young_notify ptep_test_and_clear_young #define pmdp_clear_young_notify pmdp_test_and_clear_young diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 2f0dd3a4ace1..fcf7a7820061 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -1087,6 +1087,41 @@ static inline void wrprotect_ptes(struct mm_struct *= mm, unsigned long addr, } #endif =20 +#ifndef clear_flush_young_ptes +/** + * clear_flush_young_ptes - Clear the access bit and perform a TLB flush f= or PTEs + * that map consecutive pages of the same folio. + * @vma: The virtual memory area the pages are mapped into. + * @addr: Address the first page is mapped at. + * @ptep: Page table pointer for the first entry. + * @nr: Number of entries to clear access bit. + * + * May be overridden by the architecture; otherwise, implemented as a simp= le + * loop over ptep_clear_flush_young(). + * + * Note that PTE bits in the PTE range besides the PFN can differ. For exa= mple, + * some PTEs might be write-protected. + * + * Context: The caller holds the page table lock. The PTEs map consecutive + * pages that belong to the same folio. The PTEs are all in the same PMD. + */ +static inline int clear_flush_young_ptes(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep, + unsigned int nr) +{ + int young; + + young =3D ptep_clear_flush_young(vma, addr, ptep); + while (--nr) { + ptep++; + addr +=3D PAGE_SIZE; + young |=3D ptep_clear_flush_young(vma, addr, ptep); + } + + return young; +} +#endif + /* * On some architectures hardware does not set page access bit when access= ing * memory page, it is responsibility of software setting this bit. It brin= gs diff --git a/mm/rmap.c b/mm/rmap.c index d6799afe1114..a0fc05f5966f 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -827,9 +827,11 @@ static bool folio_referenced_one(struct folio *folio, struct folio_referenced_arg *pra =3D arg; DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); int ptes =3D 0, referenced =3D 0; + unsigned int nr; =20 while (page_vma_mapped_walk(&pvmw)) { address =3D pvmw.address; + nr =3D 1; =20 if (vma->vm_flags & VM_LOCKED) { ptes++; @@ -874,9 +876,24 @@ static bool folio_referenced_one(struct folio *folio, if (lru_gen_look_around(&pvmw)) referenced++; } else if (pvmw.pte) { + if (folio_test_large(folio)) { + unsigned long end_addr =3D + pmd_addr_end(address, vma->vm_end); + unsigned int max_nr =3D + (end_addr - address) >> PAGE_SHIFT; + pte_t pteval =3D ptep_get(pvmw.pte); + + nr =3D folio_pte_batch(folio, pvmw.pte, + pteval, max_nr); + } + + ptes +=3D nr; if (ptep_clear_flush_young_notify(vma, address, - pvmw.pte)) + pvmw.pte, nr)) referenced++; + /* Skip the batched PTEs */ + pvmw.pte +=3D nr - 1; + pvmw.address +=3D (nr - 1) * PAGE_SIZE; } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { if (pmdp_clear_flush_young_notify(vma, address, pvmw.pmd)) @@ -886,7 +903,15 @@ static bool folio_referenced_one(struct folio *folio, WARN_ON_ONCE(1); } =20 - pra->mapcount--; + pra->mapcount -=3D nr; + /* + * If we are sure that we batched the entire folio, + * we can just optimize and stop right here. + */ + if (ptes =3D=3D pvmw.nr_pages) { + page_vma_mapped_walk_done(&pvmw); + break; + } } =20 if (referenced) --=20 2.47.3