From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-110.freemail.mail.aliyun.com (out30-110.freemail.mail.aliyun.com [115.124.30.110]) (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 C4F52248F54 for ; Thu, 26 Feb 2026 03:42:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.110 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772077342; cv=none; b=MeYgDFfFGaHdYkYVpQTKPrrKkODk7c7TmIsIwTw6VNfS+qRrDBaGxWHlR5WBSiGUV63pqSMocE2/c9ZTq9352ihc6g5WDH7z1a6s+tVLGqA3Bsz4N9ScNadUPVsC1eoE2pvEeJ8vQWA/PgiZuJogxrtJp0wVzuBwvJrrCpep3rU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772077342; c=relaxed/simple; bh=qjekFK0n1SFA4bilQMRJRgkAQbsh0W3YdNwkDM6kyx0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=J3gQo0ABxap7rDyXxvnQXtX6W3s9kV61zn84H9OAtEg5z6UI/9JrESA9JmjBB1aRy4RqWxjIXFN/+YN19Xo5SQ+Dp7TW0claQkbzzUJgU47LmWdPBcRCEDqGr9Qhn791oEu48ziuNeYTtkmfKjGlNVHPhnq/edZ+WGkiQ+Dgu6A= 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=BANf9/8O; arc=none smtp.client-ip=115.124.30.110 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="BANf9/8O" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1772077335; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=s/4WtA3QVEwzHgjUpBzvEPaT6QgOS9tebXTKZPMA8IU=; b=BANf9/8O1QaUdIUDXVcCYUkIzjk/afwq0niLBfkXSmXlGNZZBvshdVAOgF/Brex5TpYmQq8ScFTbXKGvDViagnuvZ/1GTlSdYJcqZfWSbMZXjCZ3RgBNlFxzHS7U2tWmnpYJv8Il0FNL5J3sJnQAv1nli6aPzoNDmjFtTa5/YnM= Received: from 30.74.144.118(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WzpnIJH_1772077332 cluster:ay36) by smtp.aliyun-inc.com; Thu, 26 Feb 2026 11:42:13 +0800 Message-ID: <32c538ce-6af8-48a8-86fc-d26ee253af54@linux.alibaba.com> Date: Thu, 26 Feb 2026 11:42:12 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] mm: add a batched helper to clear the young flag for large folios To: "David Hildenbrand (Arm)" , akpm@linux-foundation.org Cc: catalin.marinas@arm.com, will@kernel.org, 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, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/25/26 10:04 PM, David Hildenbrand (Arm) wrote: > On 2/24/26 02:56, Baolin Wang wrote: >> Currently, MGLRU will call ptep_clear_young_notify() to check and clear the >> young flag for each PTE sequentially, which is inefficient for large folios >> reclamation. >> >> Moreover, on Arm64 architecture, which supports contiguous PTEs, the Arm64- >> specific ptep_test_and_clear_young() already implements an optimization to >> clear the young flags for PTEs within a contiguous range. However, this is not >> sufficient. Similar to the Arm64 specific clear_flush_young_ptes(), we can >> extend this to perform batched operations for the entire large folio (which >> might exceed the contiguous range: CONT_PTE_SIZE). >> >> Thus, we can introduce a new batched helper: test_and_clear_young_ptes() and >> its wrapper clear_young_ptes_notify(), to perform batched checking of the young >> flags for large folios, which can help improve performance during large folio >> reclamation when MGLRU is enabled. And it will be overridden by the architecture >> that implements a more efficient batch operation in the following patches. >> > > Maybe mention that the implementation follows the other existing functions. Ack. >> Signed-off-by: Baolin Wang >> --- >> include/linux/pgtable.h | 36 ++++++++++++++++++++++++++++++++++++ >> mm/internal.h | 23 ++++++++++++++++++----- >> 2 files changed, 54 insertions(+), 5 deletions(-) >> >> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >> index 776993d4567b..0bcd3be524d3 100644 >> --- a/include/linux/pgtable.h >> +++ b/include/linux/pgtable.h >> @@ -1103,6 +1103,42 @@ static inline int clear_flush_young_ptes(struct vm_area_struct *vma, >> } >> #endif >> >> +#ifndef test_and_clear_young_ptes >> +/** >> + * test_and_clear_young_ptes - Mark PTEs that map consecutive pages of the same >> + * folio as old >> + * @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 simple >> + * loop over ptep_test_and_clear_young(). >> + * >> + * Note that PTE bits in the PTE range besides the PFN can differ. For example, >> + * some PTEs might be write-protected. > > Document the return value? > > Returns: whether any PTE was young. Ack. > > Or sth like that. > >> + * >> + * 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 test_and_clear_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, >> + unsigned int nr) > > Two tabs ... Ack. > >> +{ >> + int young = 0; >> + >> + for (;;) { >> + young |= ptep_test_and_clear_young(vma, addr, ptep); >> + if (--nr == 0) >> + break; >> + ptep++; >> + addr += PAGE_SIZE; >> + } >> + >> + return young; > > BTW: can this function simply return (and use) a bool instead? > > Likely we should do the same for the other functions, but that can be > done separately. Yes, add this to my TODO list to convert all related functions. >> /* >> * 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/internal.h b/mm/internal.h >> index 1ba175b8d4f1..1b59be99dc3f 100644 >> --- a/mm/internal.h >> +++ b/mm/internal.h >> @@ -1813,16 +1813,23 @@ static inline int pmdp_clear_flush_young_notify(struct vm_area_struct *vma, >> return young; >> } >> >> -static inline int ptep_clear_young_notify(struct vm_area_struct *vma, >> - unsigned long addr, pte_t *ptep) >> +static inline int clear_young_ptes_notify(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, >> + unsigned int nr) >> { >> int young; >> >> - young = ptep_test_and_clear_young(vma, addr, ptep); >> - young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE); >> + young = test_and_clear_young_ptes(vma, addr, ptep, nr); >> + young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + nr * PAGE_SIZE); >> return young; >> } >> >> +static inline int ptep_clear_young_notify(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep) >> +{ >> + return clear_young_ptes_notify(vma, addr, ptep, 1); >> +} >> + >> static inline int pmdp_clear_young_notify(struct vm_area_struct *vma, >> unsigned long addr, pmd_t *pmdp) >> { >> @@ -1837,9 +1844,15 @@ static inline int pmdp_clear_young_notify(struct vm_area_struct *vma, >> >> #define clear_flush_young_ptes_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 clear_young_ptes_notify test_and_clear_young_ptes >> #define pmdp_clear_young_notify pmdp_test_and_clear_young >> >> +static inline int ptep_clear_young_notify(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep) >> +{ >> + return test_and_clear_young_ptes(vma, addr, ptep, 1); >> +} > > Why not outside of the ifdef a single generic > > static inline int ptep_clear_young_notify(struct vm_area_struct *vma, > unsigned long addr, pte_t *ptep) > { > return clear_young_ptes_notify(vma, addr, ptep, 1); > } Yes, will do. And this function will be removed in the following patch.