From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 783757081E for ; Wed, 25 Feb 2026 14:04:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772028265; cv=none; b=R8tLAf+IRTH+stcnXL9XBh7r8eaEsXNTD0MRinoZkg0wmrwX3v20KASUiBICTrMFsmsYVfCLT1f703K3xjh5iEb2IR4YZGeblhcJRhyCT6boiCWjuSkv3EctgdnpSKNr85ixgR1eWchR/RZtnDnw0+ByGMjq/+BQZVRe+cxAN8s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772028265; c=relaxed/simple; bh=uGl0916oRQSQUnxyyrcUO8NjVfohNTiN1mXCplhRCQA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aFA+EWToNbiMtBii8wFSqF2pnwAcfKhcj0S8q45X1STmow4CuwaIZcqjKHdgZ9r8mdjUG05Jf+642vVsUj5J1UbEBVS+kv27b2SOb4uXmSQHMKrNHfqOmdF8rxA3YgdvR1mbmXAc4G7V6cal1pIqJBs2wa0zYbUEuruk1rETPO8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PClkNlBY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PClkNlBY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1371FC116D0; Wed, 25 Feb 2026 14:04:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772028265; bh=uGl0916oRQSQUnxyyrcUO8NjVfohNTiN1mXCplhRCQA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PClkNlBYDQ2xdogeOlwf0lwcfsg8VJYH5FB61T1LdXbnCrDvl409Q9vKrvHyWSapz 6YHimcgknAFRJHtKYdKoKu3wtkVHa0WrB6Juwh5XxqTV+O4WE4DNivfekLfdQ2Y27J Bs/XpORBfPSoslHXzkCwCQLmE6OKF0o5hV5mOrvRs6KNAcaVSLJjr7gSBQfR64L9sg JOnakNnjyfNTVutKLSaugkSwjGDg4Vj7QhjoepZRF4yfpA/fjRpxmza7KB3+D2OG14 413W7Kgem4AGvcItQtQnCP+i6sLuxBtvhXQsW8uSxM0tT3LdwjhyW3lXj84sZLb3gb 9orwgTYjnzsTw== Message-ID: Date: Wed, 25 Feb 2026 15:04:17 +0100 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: Baolin Wang , 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: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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. > 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. 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 ... > +{ > + 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. > +} > +#endif > + > /* > * 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); } Same comment regarding bool. -- Cheers, David