From nobody Sun Feb 8 15:01:28 2026 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (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 7EF603611D for ; Wed, 27 Mar 2024 09:08:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711530531; cv=none; b=GPOr30RBkQMNLSmkLn5Sj+yrlCah8OOXMTiBlfkU0zWPVmUqqJQGWB528/5TSVs+2DS5B+KR38ZJ2x5Ga4dJGr0DtW2tye/+f5PrEzUcDBAfl/iXNCUw8yzXCMMyXK1n1/UhEN98NfRIV+hE2qfdAVscUpcLH1VK0RgauY7SYmU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711530531; c=relaxed/simple; bh=/toiUyRRKpHhrNq1RW8Qw0KewFXk6dt7DT2RMe/GA2U=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=ECR/DUBm0ermn/fOUvDCyOt791bXeB5n+gGE/MGDlGCASRw0QiMYUKJ7vEBD3HtIttj1JqBGL0dyh7AxMmLlCXkRIEPTH1iVHQB4RYFhewur4Fsey811pPBuCVkSVlR36sR3ICQcLcEU2IIfWoniTjuulFKqHetGRIseBPj9rfA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.163]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4V4LQB0LQgz1xsqX; Wed, 27 Mar 2024 17:06:42 +0800 (CST) Received: from kwepemm600020.china.huawei.com (unknown [7.193.23.147]) by mail.maildlp.com (Postfix) with ESMTPS id 69422180062; Wed, 27 Mar 2024 17:08:42 +0800 (CST) Received: from localhost.localdomain (10.175.112.125) by kwepemm600020.china.huawei.com (7.193.23.147) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.35; Wed, 27 Mar 2024 17:08:41 +0800 From: Peng Zhang To: , CC: , , , , , , , , Subject: [PATCH] userfaultfd: early return in dup_userfaultfd() Date: Wed, 27 Mar 2024 17:08:35 +0800 Message-ID: <20240327090835.3232629-1-zhangpeng362@huawei.com> X-Mailer: git-send-email 2.25.1 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 X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To kwepemm600020.china.huawei.com (7.193.23.147) Content-Type: text/plain; charset="utf-8" From: ZhangPeng When vma->vm_userfaultfd_ctx.ctx is NULL, vma->vm_flags should have cleared __VM_UFFD_FLAGS. Therefore, there is no need to down_write or clear the flag, which will affect fork performance. Fix this by returning early if octx is NULL in dup_userfaultfd(). By applying this patch we can get a 1.3% performance improvement for lmbench fork_prot. Results are as follows: base early return Process fork+exit: 419.1106 413.4804 Signed-off-by: ZhangPeng Reviewed-by: Peter Xu --- fs/userfaultfd.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 60dcfafdc11a..3e6ddda6f159 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -657,7 +657,10 @@ int dup_userfaultfd(struct vm_area_struct *vma, struct= list_head *fcs) struct userfaultfd_fork_ctx *fctx; =20 octx =3D vma->vm_userfaultfd_ctx.ctx; - if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) { + if (!octx) + return 0; + + if (!(octx->features & UFFD_FEATURE_EVENT_FORK)) { vma_start_write(vma); vma->vm_userfaultfd_ctx =3D NULL_VM_UFFD_CTX; userfaultfd_set_vm_flags(vma, vma->vm_flags & ~__VM_UFFD_FLAGS); --=20 2.25.1