From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 1FB3C32D0CB for ; Thu, 18 Dec 2025 12:20:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766060420; cv=none; b=s/fZvEi38bfK7+bReZ+4VZGnStvevBctsZTbsQd2UuyCcNyk3sqEv1Zt5QnhkRWsL+/RfnKUy6b8wSq6NbD/Jt1ezGgTqmBsgXeG2L2vRBMFPi7bTT32Vz89W3RIGYKypTQ0KLnwn41Bz7xxK8IpNTjNgPgW1b+X8bHHE6fNInE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766060420; c=relaxed/simple; bh=5xLKldqpDgfsv/qgEnklJL1EPTa4Lo46Efy6yXVCqiY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IA9mAsFFAzs9PRbmjekIpa97NxbNo4tA8lZDCKiiDWL20TmNmsSLRstJCQPa/l0Jh9c372hjGyMDc/LV3Vq+GiIQqUfd7UiVSv4y4Wh5Wtb1baOqK/7z7uY4EPuULVQ26qaOQpB6UwgfoGmJuyNLLtbKuNvk+C+s7SDmLVDtvng= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3F75EFEC; Thu, 18 Dec 2025 04:20:10 -0800 (PST) Received: from [10.1.39.180] (unknown [10.1.39.180]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 929F73F762; Thu, 18 Dec 2025 04:20:14 -0800 (PST) Message-ID: Date: Thu, 18 Dec 2025 12:20:13 +0000 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 v2 1/3] arm64: mm: support batch clearing of the young flag for large folios Content-Language: en-GB To: Baolin Wang , 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, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <1beaa7de-4b31-4f19-abee-83872f868e28@arm.com> <96c0adcc-abfd-4a44-be93-1c6bd7942d6d@linux.alibaba.com> From: Ryan Roberts In-Reply-To: <96c0adcc-abfd-4a44-be93-1c6bd7942d6d@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 18/12/2025 07:15, Baolin Wang wrote: > > > On 2025/12/17 23:43, Ryan Roberts wrote: >> Sorry I'm a bit late to the party... > > Never mind. It's not late and comments are always welcome :) > >> On 11/12/2025 08:16, 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. >>> >>> 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          | 44 ++++++++++++++++++++++---------- >>>   2 files changed, 37 insertions(+), 19 deletions(-) >>> >>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >>> index 0944e296dd4a..e03034683156 100644 >>> --- a/arch/arm64/include/asm/pgtable.h >>> +++ b/arch/arm64/include/asm/pgtable.h >>> @@ -1679,10 +1679,10 @@ 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); >>> +extern int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma, >>> +                unsigned long addr, pte_t *ptep, unsigned int nr); >>> +extern int contpte_clear_flush_young_ptes(struct vm_area_struct *vma, >>> +                unsigned long addr, pte_t *ptep, unsigned int nr); >> >> The "contpte_" functions are intended to be private to the arm64 arch and should >> be exposed via the generic APIs. But I don't see any generic batched API for >> this, so you're only actually able to pass CONT_PTES as nr. Perhaps you're >> planning to define "test_and_clear_young_ptes()" and "clear_flush_young_ptes()" >> in later patches? > > Right. This is a preparation patch, and will be used in patch 2. > >>>   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, >>> @@ -1854,7 +1854,7 @@ 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); >>>   } >>>     #define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH >>> @@ -1866,7 +1866,7 @@ 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); >>>   } >>>     #define wrprotect_ptes wrprotect_ptes >>> diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c >>> index c0557945939c..19b122441be3 100644 >>> --- a/arch/arm64/mm/contpte.c >>> +++ b/arch/arm64/mm/contpte.c >>> @@ -488,8 +488,9 @@ 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 >>> @@ -500,39 +501,56 @@ int contpte_ptep_test_and_clear_young(struct >>> vm_area_struct *vma, >>>        * having to unfold. >>>        */ >>>   +    unsigned long start = addr; >> >> Personally I wouldn't bother defining start - just reuse addr. You're >> incrementing start in the below loop, so it's more appropriate to call it addr >> anyway. > > OK. > >>> +    unsigned long end = start + nr * PAGE_SIZE; >>>       int young = 0; >>>       int i; >>>   -    ptep = contpte_align_down(ptep); >>> -    addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >>> +    if (pte_cont(__ptep_get(ptep + nr - 1))) >>> +        end = ALIGN(end, CONT_PTE_SIZE); >>>   -    for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) >>> -        young |= __ptep_test_and_clear_young(vma, addr, ptep); >>> +    if (pte_cont(__ptep_get(ptep))) { >>> +        start = ALIGN_DOWN(start, CONT_PTE_SIZE); >>> +        ptep = contpte_align_down(ptep); >>> +    } >>> + >>> +    nr = (end - start) / PAGE_SIZE; >>> +    for (i = 0; i < nr; i++, ptep++, start += PAGE_SIZE) >> >> Given you're now defining end, perhaps we don't need nr? >> >>     for (; addr != end; ptep++, addr += PAGE_SIZE) >>         young |= __ptep_test_and_clear_young(vma, addr, ptep); > > Yes, good point. > >>> +        young |= __ptep_test_and_clear_young(vma, start, 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 start = addr; >>> +        unsigned long end = start + nr * PAGE_SIZE; >>> + >>> +        if (pte_cont(__ptep_get(ptep + nr - 1))) >>> +            end = ALIGN(end, CONT_PTE_SIZE); >>> + >>> +        if (pte_cont(__ptep_get(ptep))) >>> +            start = ALIGN_DOWN(start, CONT_PTE_SIZE); >>> + >> >> We now have this pattern of expanding contpte blocks up and down in 3 places. >> Perhaps create a helper? > > Sounds reasonable. How about the following helper? > > static pte_t *contpte_align_addr_ptep(unsigned long *start, unsigned long *end, >                                         pte_t *ptep, unsigned int nr) > { >         unsigned long end_addr = *start + nr * PAGE_SIZE; > >         if (pte_cont(__ptep_get(ptep + nr - 1))) I think this is safe but calling it out to check; you're not checking that the pte is valid, so theoretically you could have a swap-entry here with whatever overlays the contiguous bit set. So then you would incorrectly extend. But I think it is safe because the expectation is that core-mm has already checked that the whole range is present? >                 *end = ALIGN(end_addr, CONT_PTE_SIZE); > >         if (pte_cont(__ptep_get(ptep))) { >                 *start = ALIGN_DOWN(*start, CONT_PTE_SIZE); >                 ptep = contpte_align_down(ptep); >         } > >         return ptep; > } Looks good.