From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-99.freemail.mail.aliyun.com (out30-99.freemail.mail.aliyun.com [115.124.30.99]) (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 A233F3A1E76 for ; Thu, 25 Dec 2025 02:48:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.99 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766630935; cv=none; b=KXshJasRuwLNl0hXy24QojwN+vbHCOZoBmWPYr+I7JsP/GaOnHmMFqL8f0qyY6FaN89fpLwSe4TbasYphtBk5dBk8tOqKWZhh9D1UPhwjVmTnq8jA4kQxzVW5JNmiSLXKMPEMeB1HXzKVsrMwI5JRq5LiQogfZ73LkF6ifoT+WM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766630935; c=relaxed/simple; bh=ZndIKELVoP0AhQOY3LNsg6sIExz8xmmPrLbt/e9zVaM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gRZk4nOe1x/QisbjNv1/ICvkpI0a8CIO3rlQA9f1wfcYZSkLOJT/Jh/Sm8k4KRzaYIvG6LuDDszzq+ObuVm5G4FoMpfUKJn/3EzFh15/4Ld1Do0mRhmlnxVJzEYTGSZvBMu8O/VGSzRAxjcX13lUfy6/sblxGyORcKk78mLEoGo= ARC-Authentication-Results:i=1; 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Thu, 25 Dec 2025 10:48:43 +0800 Message-ID: <02239ca7-9701-4bfa-af0f-dcf0d05a3e89@linux.alibaba.com> Date: Thu, 25 Dec 2025 10:48:42 +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 v4 3/5] arm64: mm: support batch clearing of the young flag 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: <3b427d9010a6d52f2b91342760f12be097d21cf6.1766455378.git.baolin.wang@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2025/12/24 22:07, Ryan Roberts wrote: > On 23/12/2025 05:48, Baolin Wang wrote: >> Currently, contpte_ptep_test_and_clear_young() and contpte_ptep_clear_flush_young() >> only clear the young flag and flush TLBs for PTEs within the contiguous range. >> To support batch PTE operations for other sized large folios in the following >> patches, adding a new parameter to specify the number of PTEs that map consecutive >> pages of the same large folio in a single VMA and a single page table. >> >> While we are at it, rename the functions to maintain consistency with other >> contpte_*() functions. >> >> Signed-off-by: Baolin Wang >> --- >> arch/arm64/include/asm/pgtable.h | 12 ++++++------ >> arch/arm64/mm/contpte.c | 33 ++++++++++++++++++-------------- >> 2 files changed, 25 insertions(+), 20 deletions(-) >> >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >> index 445e18e92221..d5fbe72e820a 100644 >> --- a/arch/arm64/include/asm/pgtable.h >> +++ b/arch/arm64/include/asm/pgtable.h >> @@ -1648,10 +1648,10 @@ extern void contpte_clear_full_ptes(struct mm_struct *mm, unsigned long addr, >> extern pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm, >> unsigned long addr, pte_t *ptep, >> unsigned int nr, int full); >> -extern int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma, >> - unsigned long addr, pte_t *ptep); >> -extern int contpte_ptep_clear_flush_young(struct vm_area_struct *vma, >> - unsigned long addr, pte_t *ptep); >> +int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, unsigned int nr); >> +int contpte_clear_flush_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, unsigned int nr); >> extern void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr, >> pte_t *ptep, unsigned int nr); >> extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, >> @@ -1823,7 +1823,7 @@ static inline int ptep_test_and_clear_young(struct vm_area_struct *vma, >> if (likely(!pte_valid_cont(orig_pte))) >> return __ptep_test_and_clear_young(vma, addr, ptep); >> >> - return contpte_ptep_test_and_clear_young(vma, addr, ptep); >> + return contpte_test_and_clear_young_ptes(vma, addr, ptep, CONT_PTES); > > As per your fixup patch, I agree that nr should be 1 here, not CONT_PTES. Yes. >> } >> >> #define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH >> @@ -1835,7 +1835,7 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma, >> if (likely(!pte_valid_cont(orig_pte))) >> return __ptep_clear_flush_young(vma, addr, ptep); >> >> - return contpte_ptep_clear_flush_young(vma, addr, ptep); >> + return contpte_clear_flush_young_ptes(vma, addr, ptep, CONT_PTES); > > And same here. > >> } >> >> #define wrprotect_ptes wrprotect_ptes >> diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c >> index e4ddeb46f25d..b929a455103f 100644 >> --- a/arch/arm64/mm/contpte.c >> +++ b/arch/arm64/mm/contpte.c >> @@ -508,8 +508,9 @@ pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm, >> } >> EXPORT_SYMBOL_GPL(contpte_get_and_clear_full_ptes); >> >> -int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma, >> - unsigned long addr, pte_t *ptep) >> +int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, >> + unsigned int nr) >> { >> /* >> * ptep_clear_flush_young() technically requires us to clear the access >> @@ -518,41 +519,45 @@ int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma, >> * contig range when the range is covered by a single folio, we can get >> * away with clearing young for the whole contig range here, so we avoid >> * having to unfold. >> + * >> + * The 'nr' means consecutive (present) PTEs that map consecutive pages >> + * of the same large folio in a single VMA and a single page table. >> */ >> >> + unsigned long end = addr + nr * PAGE_SIZE; >> int young = 0; >> - int i; >> >> - ptep = contpte_align_down(ptep); >> - addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >> - >> - for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) >> + ptep = contpte_align_addr_ptep(&addr, &end, ptep, nr); >> + for (; addr != end; ptep++, addr += PAGE_SIZE) >> young |= __ptep_test_and_clear_young(vma, addr, ptep); >> >> return young; >> } >> -EXPORT_SYMBOL_GPL(contpte_ptep_test_and_clear_young); >> +EXPORT_SYMBOL_GPL(contpte_test_and_clear_young_ptes); >> >> -int contpte_ptep_clear_flush_young(struct vm_area_struct *vma, >> - unsigned long addr, pte_t *ptep) >> +int contpte_clear_flush_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, >> + unsigned int nr) >> { >> int young; >> >> - young = contpte_ptep_test_and_clear_young(vma, addr, ptep); >> + young = contpte_test_and_clear_young_ptes(vma, addr, ptep, nr); >> >> if (young) { >> + unsigned long end = addr + nr * PAGE_SIZE; >> + >> + contpte_align_addr_ptep(&addr, &end, ptep, nr); >> /* >> * See comment in __ptep_clear_flush_young(); same rationale for >> * eliding the trailing DSB applies here. >> */ >> - addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >> - __flush_tlb_range_nosync(vma->vm_mm, addr, addr + CONT_PTE_SIZE, >> + __flush_tlb_range_nosync(vma->vm_mm, addr, end, >> PAGE_SIZE, true, 3); > > Hmm... The requirement is that we must flush the _page_ if clearing access for a > pte that does not have the contiguous bit set, or we must flush the _contpte > block_ if clearing access for a pte that does have the contiguous bit set. > > With your changes, you may call for a large range that covers multiple contpte > blocks but only has a single pte in a single contpte block for which the access > bit was previously set. But that will cause flushing the TLB for the full range. > Could this cause a performance issue? Yes, no, maybe... I think it's unlikely > but I wouldn't rule it out in some edge case. > > I wonder if it's better to track the sub-ranges where access was cleared and > only issue tlbi for those sub-ranges? Probably just keep it simple (the way you > have done it) until/unless we see an actual problem? Good question. Indeed, as you said, we flush the TLB per folio now, which might increase the flush range. However, I think this approach is relatively reasonable for now. First, the mm-core also tracks the access status per folio, and it's really unnecessary to add excessive complexity to track the access status of sub-pages (or sub-ranges). I can already imagine that tracking the access status for each cont-block range as well as for non-cont pages across the entire large folio range, which can be too complicated. Second, __flush_tlb_range_nosync() is a lightweight flush. I quickly ran a measurement on my machine and found that the overhead of __flush_tlb_range_nosync() barely changes between nr=16 and nr=256 (both are around 40 ns). Therefore, I would still prefer to keep the logic here simple.