From nobody Sun Oct 5 16:18:53 2025 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) (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 84A9F8F66 for ; Thu, 31 Jul 2025 12:25:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.189 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753964720; cv=none; b=qfMVPv4twQHTFchBgH/Zanqmj33dAtQGIHSp8JeYi8OlNXVgVMkUFiML0zv2c4XtYFfKYQ97hx9fGaFQgJmyWgHWwct08ac68MXcmTwbJuDECu8O+CWdcvF/E11odkA6AdbNE6QaIJA+IxRgUQG5tUTmDDhSQJurk5H3KmZvWpo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753964720; c=relaxed/simple; bh=ne/wEhm2SsX3GajukXHa6Bh4mXJyWnemx4jMRZuVa00=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=NYoHul6EzvmUFmGvo5nYQdHbr2gaDJ7TLPBthrde4PV9y8qxnZVSasQ2UVUk3KyN94RZY4vh1eNzZX1jTTskytNTk26pGzYExIPikDli0PLgzOR9+HgwzIByvtx7j8OJd2d+fSHTgKhB++Wi2qU05mgP8yDeirc6xniGvTV5m7Y= 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=45.249.212.189 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 [172.19.163.48]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4bt7Td12hlzPtBZ; Thu, 31 Jul 2025 20:20:53 +0800 (CST) Received: from dggpemf500012.china.huawei.com (unknown [7.185.36.8]) by mail.maildlp.com (Postfix) with ESMTPS id 3400918007F; Thu, 31 Jul 2025 20:25:07 +0800 (CST) Received: from huawei.com (10.175.124.71) by dggpemf500012.china.huawei.com (7.185.36.8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Thu, 31 Jul 2025 20:25:06 +0800 From: Zhang Qilong To: , , CC: , , , , , Zhang Qilong , David Hildenbrand Subject: [PATCH v4] /dev/zero: try to align PMD_SIZE for private mapping Date: Thu, 31 Jul 2025 20:23:05 +0800 Message-ID: <20250731122305.2669090-1-zhangqilong3@huawei.com> X-Mailer: git-send-email 2.43.0 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: kwepems500001.china.huawei.com (7.221.188.70) To dggpemf500012.china.huawei.com (7.185.36.8) Content-Type: text/plain; charset="utf-8" Attempt to map aligned to huge page size for private mapping which could achieve performance gains, the mprot_tw4m in libMicro average execution time on arm64: - Test case: mprot_tw4m - Before the patch: 22 us - After the patch: 17 us If THP config is not set, we fall back to system page size mappings. Reviewed-by: Lorenzo Stoakes Tested-by: Lorenzo Stoakes Acked-by: David Hildenbrand Signed-off-by: Zhang Qilong --- v4: - collect Tested-by and Reviewed-by - add comment for CONFIG_MMU #endif v3: - collect Acked-by - factor out the #ifdef CONFIG_MMU in get_unmapped_area_zero(), per Lorenzo - explicitly use #ifdef CONFIG_TRANSPARENT_HUGEPAGE, per Lorenzo and Matthew v2: - add comments on code suggested by Lorenzo - use IS_ENABLED to check THP config drivers/char/mem.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 48839958b0b1..34b815901b20 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -510,31 +510,44 @@ static int mmap_zero(struct file *file, struct vm_are= a_struct *vma) return shmem_zero_setup(vma); vma_set_anonymous(vma); return 0; } =20 +#ifndef CONFIG_MMU +static unsigned long get_unmapped_area_zero(struct file *file, + unsigned long addr, unsigned long len, + unsigned long pgoff, unsigned long flags) +{ + return -ENOSYS; +} +#else static unsigned long get_unmapped_area_zero(struct file *file, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags) { -#ifdef CONFIG_MMU if (flags & MAP_SHARED) { /* * mmap_zero() will call shmem_zero_setup() to create a file, * so use shmem's get_unmapped_area in case it can be huge; * and pass NULL for file as in mmap.c's get_unmapped_area(), * so as not to confuse shmem with our handle on "/dev/zero". */ return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags); } =20 - /* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */ - return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags); + /* + * Otherwise flags & MAP_PRIVATE: with no shmem object beneath it, + * attempt to map aligned to huge page size if possible, otherwise we + * fall back to system page size mappings. + */ +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + return thp_get_unmapped_area(file, addr, len, pgoff, flags); #else - return -ENOSYS; + return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags); #endif } +#endif /* CONFIG_MMU */ =20 static ssize_t write_full(struct file *file, const char __user *buf, size_t count, loff_t *ppos) { return -ENOSPC; --=20 2.43.0