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b=tMLkseGIapPUs6MMj3V/MMkcUxYOIwiypM8y1icvH/kbDszEtwkkcS6X3on18Q5bE5+DLYWdIiFhxZKZJ7N0QObPwE5AEFzaC5CHnjM0WccDJkwCGwVFSSDusmPvG5m8cxQSOnh/SLT2bfA6ZdcPtI+HXr62x1nD0fOGg8/+to4= Received: from 30.74.144.121(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Wvci210_1766624507 cluster:ay36) by smtp.aliyun-inc.com; Thu, 25 Dec 2025 09:01:48 +0800 Message-ID: <43b6ef51-c88f-4b0c-b512-c7195afdd31b@linux.alibaba.com> Date: Thu, 25 Dec 2025 09:01:47 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/5] mm: rmap: support batched checks of the references for large folios To: Ryan Roberts , akpm@linux-foundation.org, david@kernel.org, catalin.marinas@arm.com, will@kernel.org Cc: lorenzo.stoakes@oracle.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, 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 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 4ED1180007 X-Stat-Signature: o747atqhfqx448yujyr8bq6weryowxp4 X-HE-Tag: 1766624511-248301 X-HE-Meta: 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 yNRyyvFk hY51T4rpjI1lBq86ude8jjakFOk/UqcmumtyHAyFeb1ONVDTbBI68CK7XgM4E8jfR/uxYMGz8eL7OS7E4HyXV/ptfJcbEYhyDCzdZuMlU+eY21PLNYbKDfsPrJh98qAr1hLpzJ2R85Kx7VipGxNSAV6tq8jn6sOa7bYtRfovcC3/PxmIl3oKa51lfrOcXhGkL7ojoK5oEfolSD8+xVMjRHWYwDI5HpMek5Nskt/IQ+uD3IFfGkdheRSQrauDTBPICwEX9KwnG1qRdfmeP05zeKZkVT+bfjrPBCpAkLOsmayXBQg71FKISG2r+UOzBZ+WbPF4Qu/KJhOxCH1RFHnHuseGhZzo8eOd5vvunCkapSHXRSj6Zq0gWLWxJ6cXAvHw/JJXjiqNECYbkmHM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Ryan, On 2025/12/24 21:24, Ryan Roberts wrote: > On 23/12/2025 05:48, Baolin Wang wrote: >> 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 already >> 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 operations >> for the entire large folio (which might exceed the contiguous range: CONT_PTE_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 architecture >> that implements a more efficient batch operation in the following patches. >> >> Signed-off-by: Baolin Wang > > With the 2 niggles below addressed: > > Reviewed-by: Ryan Roberts Thanks. >> --- >> 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 = owner; >> } >> >> -#define ptep_clear_flush_young_notify(__vma, __address, __ptep) \ >> +#define ptep_clear_flush_young_notify(__vma, __address, __ptep, __nr) \ > > I think I previously suggested that this should be renamed to > clear_flush_young_ptes_notify() given that it is now a batch operation. Were > others against that or did you forget? Sorry, I missed this comment. Yes, sounds reasonable to me. Will do in the next version. >> ({ \ >> int __young; \ >> struct vm_area_struct *___vma = __vma; \ >> unsigned long ___address = __address; \ >> - __young = ptep_clear_flush_young(___vma, ___address, __ptep); \ >> + unsigned int ___nr = __nr; \ >> + __young = clear_flush_young_ptes(___vma, ___address, __ptep, ___nr); \ >> __young |= mmu_notifier_clear_flush_young(___vma->vm_mm, \ >> ___address, \ >> ___address + \ >> - PAGE_SIZE); \ >> + ___nr * PAGE_SIZE); \ >> __young; \ >> }) >> >> @@ -650,7 +651,7 @@ static inline void mmu_notifier_subscriptions_destroy(struct mm_struct *mm) >> >> #define mmu_notifier_range_update_to_read_only(r) false >> >> -#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 >> >> +#ifndef clear_flush_young_ptes >> +/** >> + * clear_flush_young_ptes - Clear the access bit and perform a TLB flush for 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 simple >> + * loop over ptep_clear_flush_young(). >> + * >> + * Note that PTE bits in the PTE range besides the PFN can differ. For example, >> + * 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 = ptep_clear_flush_young(vma, addr, ptep); >> + while (--nr) { >> + ptep++; >> + addr += PAGE_SIZE; >> + young |= ptep_clear_flush_young(vma, addr, ptep); >> + } > > I think it's better to avoid the two ptep_clear_flush_young() calls if we can. > Personally I think we should just go for the simple: > > for (i = 0; i < nr; ++i, ++ptep, addr += PAGE_SIZE) > young |= ptep_clear_flush_young(vma, addr, ptep); ACK. Thanks for reviewing.