From nobody Wed Dec 17 18:12:22 2025 Received: from mail-wm1-f48.google.com (mail-wm1-f48.google.com [209.85.128.48]) (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 BF6D93AC1C for ; Thu, 2 Oct 2025 07:35:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.48 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759390515; cv=none; b=bfgM2+kPd5ORNKmqjSMVPJyUZrB9qUwVtzu2PRfPNuy9wGHPoxH+KbR9IuwF5qBeF1DQ1M5x30NZ4BPMlEdvR45VCltUJEOfuw3374+WGPo2Q8mjW6r7VLh+xhh6mbaYN7XjTpTiYRkP8l/63I7cTGDL23kuhMZKzR4v4K7YUTI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759390515; c=relaxed/simple; bh=hpOQoDd/rDbG65uJbBFqF8tifmj75MN2LZv9tHWBIUA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ppOghqFD+tm1R939I9eOKLJxfR6gShuMdQuub7cqWwkTeXrSJmSpJ41TXcqkv9mnbgvQxtJTi13oZsgTtedZ5fkUWrQQBiH6Xt7mDnHyGyj/aA2N+Jv/x+ZPI1JTUihgoUAWZrvsIkuBQ7qVXNlgzsEnbUx227ykC8wMyUGdXBw= 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=209.85.128.48 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-f48.google.com with SMTP id 5b1f17b1804b1-46e491a5b96so3793865e9.2 for ; Thu, 02 Oct 2025 00:35:13 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1759390512; x=1759995312; 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=VRXzbaSJvEeEuAD//MreCCVgmlc+Vr7UAiNsZmiYS+g=; b=hDtuOS6TfdIpSkK0NRxHLmjWYVJQXejaMcjyzC9LGLHch6mtXBPalfNsALpt7xTbbd RGXc7smpwT0jn2QYO3i0o4WaUQXQ1X5uwr7xefmz894HRqlchlfT7Qk0qwvK5nSKQZcX HQYxn0tF0x0EqUXjS4MbefpDiPDkwQLkp98gkQE+USEHO5p7kNAWIH3xAGgua6LcsN67 S700Ik6ukv7D0vTLxm3VCAzj3uDlUI6TRB90r5dDIrA0ModZ3kzawa1kmX1qqcx/ln3p c57Z5BylWxh5dWsDhRNXztAJo1FMwe0nYO1/FnQ9F2TPB4hQ7eJ0jwP//MPSJhU2WuXE /prQ== X-Forwarded-Encrypted: i=1; AJvYcCXsTkp/rSzOnASZ30mAtb0L+XV8fyZAcBzt5jMB12EIWupPsDdpNstyxtuRFbHOw1INVEqOznoDsorHBrY=@vger.kernel.org X-Gm-Message-State: AOJu0Yycay195sN71uL/IL5I8AziP5ESe5FsiOIfFyzPo8apEPitVTI8 vo0mkoB2s5baCRMDrG/N5hTJRyXDLIZyaRA1vZ/fVyiEgbHrE+etVlqD X-Gm-Gg: ASbGnctrm+ujvfVanWd/pYzAPJFrJK7L8H5+BiapP7IZv3rq8Hxq6E2Vi4Ey7h9QYzs tKZpsVMP46qTRnSwSDdsa0IEp7XcpqH0sfmXAwInkHjKgIIF0Hb85QjH2tD0BUEfzDhUkQPpBf1 GCS2n5rzF0LyBsgreGxLqDxOU9N2FMkSS2lKvNICNP9LI+XI4iaRkBjTADf5uKlQVoL7uGAdB4h GwKjLGKkQD7nBtShMpxqXiun1KohdJAZhTw1ODbZxsticAScxIM50NcpFGB6BDgnW9DsEKxA5/f gF8gkc2lBmE7y+8bdsVXIHkiOf6NTCD1E/pqInpOXslhwen0ObbFb7vQzmG/RM7QDkjlQYytg4i V28wax0yNC5KoXgSWJtVTwKSDwr9zgZ9HzPXJ6R4= X-Google-Smtp-Source: AGHT+IG2jlLDIgDG0wBkYWool7Xk9VaM4c6zOW54Z9lnjZVwUFDfiLKSLmpYXXdi82tG9D7HIgWkzg== X-Received: by 2002:a05:600c:64ce:b0:46e:32dd:1b1a with SMTP id 5b1f17b1804b1-46e61262498mr50328435e9.7.1759390511979; Thu, 02 Oct 2025 00:35:11 -0700 (PDT) Received: from localhost.localdomain ([2a09:0:1:2::301b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e6a692af6sm17856135e9.21.2025.10.02.00.35.07 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 02 Oct 2025 00:35:11 -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 1/2] mm/khugepaged: optimize PTE scanning with if-else-if-else-if chain Date: Thu, 2 Oct 2025 15:32:54 +0800 Message-ID: <20251002073255.14867-2-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20251002073255.14867-1-lance.yang@linux.dev> References: <20251002073255.14867-1-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. 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. Suggested-by: Dev Jain Suggested-by: David Hildenbrand Signed-off-by: Lance Yang Reviewed-by: Dev Jain Reviewed-by: Wei 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