From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 68101D64062 for ; Wed, 17 Dec 2025 06:44:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=k11HXNGhgQ+qa2nrzsTblXusICoL85lOX63vXQEX4po=; b=xQhG30RNeYcJlEM+bfwO+L1Pb6 2vBChdVOp92ndJrYf+pqOtBN3Iv89RSSHRxfIW7Yw6fgkUJFvEOgmdwqn0inLe+kXcOhpPIHwKEXK TCQvArGW/ucLM0qPPDmgkOkKyBQTrcrA1Ut0RFnybnK7DCBmoMCi2H1x70Mn328CpMFet8rgApxbs TRz7gwfhxVSkRk+yDhXVi3fCqhWkCfqIXWerEQersi9zwrVaWVGZyKgWkByjUH3VaD0L2CImiuylj O7mn+qnWgCMr4w3nv5zNYcrm0zr3RFsV7caUpQiO8M7e++BlQH5513I0Ug9pu3z1UQ3zHyHrfd7uL yIhGn8Wg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vVlHB-00000006Fwi-3iib; Wed, 17 Dec 2025 06:44:46 +0000 Received: from out30-113.freemail.mail.aliyun.com ([115.124.30.113]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vVlH7-00000006FwO-0D4D for linux-arm-kernel@lists.infradead.org; Wed, 17 Dec 2025 06:44:44 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1765953877; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=k11HXNGhgQ+qa2nrzsTblXusICoL85lOX63vXQEX4po=; b=i98e2fhuhRGcYX94WtYr4mKUWa+NBGcdioqdQsLsbiFzU7NSmUXkbjpOWeHiu7kCsw/UgjkI58WDFWiNiB/GF14pWUHyxnPS2JRtJyNaEaFSWTXHk9ninc2iw8VQWftWqkPVeoK3NbXEIGC2zQs0vArL/KG7BR58SadwBOmlApg= Received: from 30.74.144.118(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Wv2EYSN_1765953875 cluster:ay36) by smtp.aliyun-inc.com; Wed, 17 Dec 2025 14:44:36 +0800 Message-ID: Date: Wed, 17 Dec 2025 14:44:34 +0800 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> <17380b96-3a9e-46f9-b22b-0e770f7f1b4f@arm.com> From: Baolin Wang In-Reply-To: <17380b96-3a9e-46f9-b22b-0e770f7f1b4f@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251216_224442_406493_72117AAF X-CRM114-Status: GOOD ( 15.16 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2025/12/17 14:23, 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; \ >> }) > > Do we have an existing bug here, in that mmu_notifier_clear_flush_young() should > have been called for CONT_PTES length if the folio was contpte mapped? I can't call it a bug, because folio_referenced_one() does iterate through each PTE of the large folio, but it is indeed inefficient.