From nobody Mon Dec 8 04:33:45 2025 Received: from mail-wm1-f53.google.com (mail-wm1-f53.google.com [209.85.128.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DE7E42D238B for ; Mon, 6 Oct 2025 14:46:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.53 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759761970; cv=none; b=g8p6OOza8Ya/kicCIPRUSOF9IAUHx+ae1Z4C6whkSDWjkLcYXpCih5y7TVxhU3gyX26G414cb4mOp6ccKF2wuaCM9J7/rBuabi7Y2UBr4tpMS/mxAJWDgsvALxCe6KxXh5ACAueBnTOU3P0bqaKH4b1cC1VGNAyKMXiZ4s5HyXU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759761970; c=relaxed/simple; bh=0Kj1bUsArtK+3VWL9yP8YhDmKf3J+wwRDa8rid9aXjk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FEky3Eeh/PjVVjC2rLJVdT828aqrMBT2q5aTWxXuR7UOg7WOBenrNJLSPm4s+jC3YEd/vl1YlJxfKT9yxaIK6m4GujGb0W8Eyx4HLq+VKP2W3yBFbiRs7TIIDef9XJ4syqi0IUvbzyCy2NE5LNIGVL831KcMGpkWSxRqmdDmSy0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=gmail.com; arc=none smtp.client-ip=209.85.128.53 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-wm1-f53.google.com with SMTP id 5b1f17b1804b1-46e430494ccso29713685e9.1 for ; Mon, 06 Oct 2025 07:46:07 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1759761966; x=1760366766; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=MtaiocTtP0D1d6fsZBlllxYLh2dMPWNbD897f/VONZw=; b=N8BKnmLSzXx0VNcu9Af2m8XAm5ZXsmkBY47fvidvOrkxkkAbsV0YN4i5xL2zdl9XF1 vn2liKYyx41ueF9Tm2+z806RVl0kLrf4aH1gIeSZSGgT1PTZhO66I+Xupms0PfJ6QxN5 /5oiyUhExSgePSVgC0ikSD4lfgBQ2W7HwpX/Tm6AnwxBt6bitRGxwMWc4gheoH7x+Hf5 vnXZ1HVnejtG1seCodenpa//4cg4N2RTVmXXMJ58B67meclkVYRjJ//q1DFDwZBXm5b9 oUAWpuR4MuVc/iMTOzkQO6Ls13z4sobPmPI55fnKM6BntnRs/Xd5SaMVtCYBrhFE2zKO rH7g== X-Forwarded-Encrypted: i=1; AJvYcCVuHSFeiHrdjcEOpDUqN3klZenRs88jH9DPNIlOv1Fp7jd//HtBGd3p61XbkD4zJvHSSyDGJ+HY8h6JHkk=@vger.kernel.org X-Gm-Message-State: AOJu0Ywpmlo2Nv5Q08woa4lcakYswms5wSnMhDGvJ+g3var9vBcCOrxD xLEQtNuAN35Smt/6FaggxrLjSkWpAoHBq9drmhMHOYiFNtfL9E7YSGVo X-Gm-Gg: ASbGncveQLRtweFrXwYEvbbHY7yWQZAQGLb/QivmDi3uk6Xc7Gb3ybZ94y41akQcnZS Ujx6d7QxxpxvktIsrCoVg0AGG6BzVm9haB42FRjEtbb2YooZXXaRlhG1CICJbJcHeDxS4AT4BtJ /hznowNDktz5bpAQGRL/LuzT8ULv1Mx0sB8CeOSOEQd2uMZBx3wOyl/ERNaN23kbekLKx2gx+kV Qh3kUQ8KwdzsscBou2RCMx4cXz+vtapQBlOYdB72oF9FDD0NxgW5UZbxoP8JjNVkSE9YUfFhDka bMNlQlFdDXWpEgDlBwtu8vzevwBrk7Gi0wOJnyMNBfZx09viRAzfNk24+OQIrp7IDZ5imsGjmNA F7ZNbtOqOvWsbbaErH3DUQSvWM+j+DC6WHFF/CMyTuI2qtPRBNA== X-Google-Smtp-Source: AGHT+IF5uSZFkd92taI4AFZxuPXGqPv0vhx+0DNW9NrjZaWgfPJ++05mIEV+P/lyyp+2PlV1EUb0qQ== X-Received: by 2002:a05:6000:2dc3:b0:3f7:b7ac:f3d2 with SMTP id ffacd0b85a97d-425671ab145mr8359436f8f.43.1759761965933; Mon, 06 Oct 2025 07:46:05 -0700 (PDT) Received: from localhost.localdomain ([2a09:0:1:2::301b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4255d8ab8b0sm21242624f8f.18.2025.10.06.07.46.02 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 06 Oct 2025 07:46:05 -0700 (PDT) From: Lance Yang To: akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, ioworker0@gmail.com, richard.weiyang@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Lance Yang Subject: [PATCH mm-new v2 1/3] mm/khugepaged: optimize PTE scanning with if-else-if-else-if chain Date: Mon, 6 Oct 2025 22:43:36 +0800 Message-ID: <20251006144338.96519-2-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20251006144338.96519-1-lance.yang@linux.dev> References: <20251006144338.96519-1-lance.yang@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Lance Yang As pointed out by Dev, the PTE checks for disjoint conditions in the scanning loops can be optimized. is_swap_pte, (pte_none && is_zero_pfn), and pte_uffd_wp are mutually exclusive. This patch refactors the loops in both __collapse_huge_page_isolate() and hpage_collapse_scan_pmd() to use a continuous if-else-if-else-if chain instead of separate if blocks. While at it, the redundant pte_present() check before is_zero_pfn() is also removed. Also, this is a preparatory step to make it easier to merge the almost-duplicated scanning logic in these two functions, as suggested by David. Reviewed-by: Wei Yang Reviewed-by: Dev Jain Reviewed-by: Zi Yan Suggested-by: Dev Jain Suggested-by: David Hildenbrand Signed-off-by: Lance Yang --- mm/khugepaged.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index f4f57ba69d72..808523f92c7b 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -548,8 +548,7 @@ static int __collapse_huge_page_isolate(struct vm_area_= struct *vma, for (_pte =3D pte; _pte < pte + HPAGE_PMD_NR; _pte++, addr +=3D PAGE_SIZE) { pte_t pteval =3D ptep_get(_pte); - if (pte_none(pteval) || (pte_present(pteval) && - is_zero_pfn(pte_pfn(pteval)))) { + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { ++none_or_zero; if (!userfaultfd_armed(vma) && (!cc->is_khugepaged || @@ -560,12 +559,10 @@ static int __collapse_huge_page_isolate(struct vm_are= a_struct *vma, count_vm_event(THP_SCAN_EXCEED_NONE_PTE); goto out; } - } - if (!pte_present(pteval)) { + } else if (!pte_present(pteval)) { result =3D SCAN_PTE_NON_PRESENT; goto out; - } - if (pte_uffd_wp(pteval)) { + } else if (pte_uffd_wp(pteval)) { result =3D SCAN_PTE_UFFD_WP; goto out; } @@ -1316,8 +1313,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *= mm, count_vm_event(THP_SCAN_EXCEED_SWAP_PTE); goto out_unmap; } - } - if (pte_uffd_wp(pteval)) { + } else if (pte_uffd_wp(pteval)) { /* * Don't collapse the page if any of the small * PTEs are armed with uffd write protection. --=20 2.49.0