From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-119.freemail.mail.aliyun.com (out30-119.freemail.mail.aliyun.com [115.124.30.119]) (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 C40C62EBDEB for ; Wed, 17 Dec 2025 07:09:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.119 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765955395; cv=none; b=TIDhbPy2j31BmVzYb4aG4cl9f2TKSy18kiJk3Ir8ly9cAckKWNuBLsg2NWm+HeH4KMqctA50mOqyIOnXMfP6VjkBXG7xxDelqD7iV1+SRd8d9Ab7TsPAja8LwRvafbnEDAUaywqSS6YhZfMqd13SCfNkj9LaZ94NY+EEOiuf+JA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765955395; c=relaxed/simple; bh=to5MYlyyoTcKN0Td0+RvfVjJ7NCQWFUueMHQOoWgz1g=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YYYc83buRV4LrhYptQFCUQc/Kdff7cFiEX3HNWpbONtcBdbaE58vagbDWFCR94ymuWsgVBdz1isLtDVKEEUI6R0XUsGvda8zKc6Y1fBED0Axl/O3qxmDsii+QOnyGRAbYTBc+igm38rpx3fV2Z6Qa8hJysWTqb8du8ZZIXuoswU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=D7Pmc0GH; arc=none smtp.client-ip=115.124.30.119 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="D7Pmc0GH" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1765955390; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=BPdhN2PgYo+tFQS6gBLjYcRITKQ82W662MYUF3IclR8=; b=D7Pmc0GHxs1MtxQ+mUUSKSvJBuwg0uA1EVb2nd2B+q45tPCELuhW/voxFq0tLm/k9yGhWBGJf7sETD5MVkPOZDLYuQB/ZqMs35iPXJAfLL2NOUF1IO1MY+HpRo7ZcgxoZ6pBeN3dueU834CAvQt+9MYNsqmf+SFW5YSmM/WtyIs= Received: from 30.74.144.118(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Wv2U.eU_1765955387 cluster:ay36) by smtp.aliyun-inc.com; Wed, 17 Dec 2025 15:09:48 +0800 Message-ID: <753ee7bd-8c9a-4242-a216-98defcd8280f@linux.alibaba.com> Date: Wed, 17 Dec 2025 15:09:47 +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 v2 2/3] mm: rmap: support batched checks of the references for large folios To: Dev Jain , akpm@linux-foundation.org, david@kernel.org, catalin.marinas@arm.com, will@kernel.org Cc: 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, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <545dba5e899634bc6c8ca782417d16fef3bd049f.1765439381.git.baolin.wang@linux.alibaba.com> <52ed7e12-b32e-4a73-ba55-eed993b930b9@arm.com> From: Baolin Wang In-Reply-To: <52ed7e12-b32e-4a73-ba55-eed993b930b9@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2025/12/17 14:49, Dev Jain wrote: > > On 11/12/25 1:46 pm, 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 Arm 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. >> >> Performance testing: >> Allocate 10G clean file-backed folios by mmap() in a memory cgroup, and try to >> reclaim 8G file-backed folios via the memory.reclaim interface. I can observe >> 33% performance improvement on my Arm64 32-core server (and 10%+ improvement >> on my X86 machine). Meanwhile, the hotspot folio_check_references() dropped >> from approximately 35% to around 5%. >> >> W/o patchset: >> real 0m1.518s >> user 0m0.000s >> sys 0m1.518s >> >> W/ patchset: >> real 0m1.018s >> user 0m0.000s >> sys 0m1.018s >> >> Signed-off-by: Baolin Wang >> --- >> arch/arm64/include/asm/pgtable.h | 11 +++++++++++ >> include/linux/mmu_notifier.h | 9 +++++---- >> include/linux/pgtable.h | 19 +++++++++++++++++++ >> mm/rmap.c | 22 ++++++++++++++++++++-- >> 4 files changed, 55 insertions(+), 6 deletions(-) >> >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >> index e03034683156..a865bd8c46a3 100644 >> --- a/arch/arm64/include/asm/pgtable.h >> +++ b/arch/arm64/include/asm/pgtable.h >> @@ -1869,6 +1869,17 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma, >> return contpte_clear_flush_young_ptes(vma, addr, ptep, CONT_PTES); >> } >> >> +#define clear_flush_young_ptes clear_flush_young_ptes >> +static inline int clear_flush_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, >> + unsigned int nr) >> +{ >> + if (likely(nr == 1)) >> + return __ptep_clear_flush_young(vma, addr, ptep); >> + >> + return contpte_clear_flush_young_ptes(vma, addr, ptep, nr); >> +} >> + >> #define wrprotect_ptes wrprotect_ptes >> static __always_inline void wrprotect_ptes(struct mm_struct *mm, >> unsigned long addr, pte_t *ptep, unsigned int nr) >> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h >> index d1094c2d5fb6..be594b274729 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) \ >> ({ \ >> 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 b13b6f42be3c..c7d0fd228cb7 100644 >> --- a/include/linux/pgtable.h >> +++ b/include/linux/pgtable.h >> @@ -947,6 +947,25 @@ static inline void wrprotect_ptes(struct mm_struct *mm, unsigned long addr, >> } >> #endif >> >> +#ifndef clear_flush_young_ptes >> +static inline int clear_flush_young_ptes(struct vm_area_struct *vma, >> + unsigned long addr, pte_t *ptep, >> + unsigned int nr) >> +{ >> + int young = 0; >> + >> + for (;;) { >> + young |= ptep_clear_flush_young(vma, addr, ptep); >> + if (--nr == 0) >> + break; >> + ptep++; >> + addr += PAGE_SIZE; >> + } >> + >> + return young; >> +} >> +#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/rmap.c b/mm/rmap.c >> index d6799afe1114..ec232165c47d 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -827,9 +827,11 @@ static bool folio_referenced_one(struct folio *folio, >> struct folio_referenced_arg *pra = arg; >> DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); >> int ptes = 0, referenced = 0; >> + unsigned int nr; >> >> while (page_vma_mapped_walk(&pvmw)) { >> address = pvmw.address; >> + nr = 1; >> >> if (vma->vm_flags & VM_LOCKED) { >> ptes++; >> @@ -874,9 +876,21 @@ static bool folio_referenced_one(struct folio *folio, >> if (lru_gen_look_around(&pvmw)) >> referenced++; >> } else if (pvmw.pte) { >> + if (folio_test_large(folio)) { >> + unsigned long end_addr = pmd_addr_end(address, vma->vm_end); > > I may be hallucinating here but I am just trying to recall things - is this a bug in > folio_pte_batch_flags()? A folio may not be naturally aligned in virtual space and hence > we may cross the PTE table while batching across it, which can be fixed by taking into > account pmd_addr_end() while computing max_nr. IMHO, the comments for the folio_pte_batch_flags() function have already made clear requirements for the caller to avoid such situations: " * @ptep must map any page of the folio. max_nr must be at least one and * must be limited by the caller so scanning cannot exceed a single VMA and * a single page table. " Additionally, Lance recently fixed a similar issue, see commit ddd05742b45b ("mm/rmap: fix potential out-of-bounds page table access during batched unmap").