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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 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 X-Rspamd-Queue-Id: 470FB1C0008 X-Stat-Signature: 47r1omibhdujuz7afgaauxfbbxhr8gq5 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1772028266-504958 X-HE-Meta: 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 z4a9UeKt MIbmklPWf311G+5Kn1+AuV3Na90Fqk9qxNNNada9xMlhKW9X/e3MEqco+NS+lss02+wttAPFGteZkkUzOR52HCyEMPJCEBbii43Xux7YKS0r/Asng1mo1yOV20kHlSPof9jNNMUA1utllUa8UgyagiMLSwjux8whhfrXd6M7YI1UbGKLXh587GBtmRuLTEKKzK0NYCWlNF930DboiXWEgDO7AH1LcBy8JthTs4ma28ZQkxcRgr/vX7bXb8P4GEpMixxZ/r9QKrYNHjZTjIZ7t1Bwd73b1gKAAcyaReBGbJLfpab6615I2oUr6lg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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