From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 7DD0B2690EC; Fri, 19 Dec 2025 08:29:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766132952; cv=none; b=PJ/Aet63bPY8hjV66KFaq8/1vm5E7WeGTmkHLtslfD3yAQw5903x7LC+Duf0YxKdMNpdovhfP9C7elRyNdOi7vouFdxF3JoOy6LsmIKU5wy0XZX7ZGq/SltMv7gaQNNt/RY34ZUcjXIJ5mslZ7gObnhTSkoM28bM4/vRboBDVAQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766132952; c=relaxed/simple; bh=UCFnBOrzhV3jWI43ElU9t2h6igr0WlVvCIX4xGYLDk0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=k3flLRX30NKtQEe2+vxws4L4M4g4Z3acOtfIbMn8A2W0wwYTjUVT9ybhxKyLmMOYiSk/DbbO9PuSVafucPg7CuEZqItyxBlbK1F5jfRE1/+lK5Vi7KX/9o0V2CqhkgOPvHLU6m/tZusJA0XcpthgwsKtlGuZ9IJb8fd3qenWT74= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jWk8hALG; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jWk8hALG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BD61DC116B1; Fri, 19 Dec 2025 08:29:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766132952; bh=UCFnBOrzhV3jWI43ElU9t2h6igr0WlVvCIX4xGYLDk0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=jWk8hALGXyTDQTBOou4ixavX7CnsUIfth0+Lxjb9cqp3NQS5XoFaSEdUdUUI+f928 jty2G8rmU7Gk/BheKCFqD9Y2FzPRO1gtYzRCpdzGkQXIilkAMjttsvH6lJ2zgEypej HaNcmYcLBoIxorXioJAgzgi2cVrlTLBJwzn0SFdSdFWPLklS7V7IbR0R+BxwEnScWT UDDL+O12Zz9/L2S6Pp283WNMS6r2C3wwlFnSfs/Y0hhmBVkNgr6FpGP5Ndo51jWUOd tqdy2GTXFYZr9jJINvQ81sVj6hCr6k9c3uf0AYlxm0bXd/uz0KlJzLGCbhDCkVDr5W WP5UqAVOuYtdw== Message-ID: Date: Fri, 19 Dec 2025 09:29:06 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/4] selftests/mm: fix faulting-in code in pagemap_ioctl test To: Kevin Brodsky , Ryan Roberts , linux-mm@kvack.org, linux-kselftest@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Mark Brown , Shuah Khan , Usama Anjum References: <20251216142633.2401447-1-kevin.brodsky@arm.com> <20251216142633.2401447-4-kevin.brodsky@arm.com> <37210500-6f6e-46ac-ac2f-ac996308590d@arm.com> <6aa47cdb-d2e7-4977-929b-7019b6f991c1@kernel.org> <0575bcf6-c1a3-4ebf-a199-3113758fbdc5@arm.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <0575bcf6-c1a3-4ebf-a199-3113758fbdc5@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 12/18/25 14:18, Kevin Brodsky wrote: > On 18/12/2025 09:05, David Hildenbrand (Red Hat) wrote: >> On 12/16/25 15:56, Ryan Roberts wrote: >>> On 16/12/2025 14:26, Kevin Brodsky wrote: >>>> One of the pagemap_ioctl tests attempts to fault in pages by >>>> memcpy()'ing them to an unused buffer. This probably worked >>>> originally, but since commit 46036188ea1f ("selftests/mm: build with >>>> -O2") the compiler is free to optimise away that unused buffer and >>>> the memcpy() with it. As a result there might not be any resident >>>> page in the mapping and the test may fail. >>>> >>>> We don't need to copy all that memory anyway. Just fault in every >>>> page by forcing the compiler to read the first byte. >>>> >>>> Cc: Usama Anjum >>>> Signed-off-by: Kevin Brodsky >>>> --- >>>>   tools/testing/selftests/mm/pagemap_ioctl.c | 6 +++--- >>>>   1 file changed, 3 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c >>>> b/tools/testing/selftests/mm/pagemap_ioctl.c >>>> index 2cb5441f29c7..67a7a3705604 100644 >>>> --- a/tools/testing/selftests/mm/pagemap_ioctl.c >>>> +++ b/tools/testing/selftests/mm/pagemap_ioctl.c >>>> @@ -1056,7 +1056,6 @@ int sanity_tests(void) >>>>       struct page_region *vec; >>>>       char *mem, *fmem; >>>>       struct stat sbuf; >>>> -    char *tmp_buf; >>>>         /* 1. wrong operation */ >>>>       mem_size = 10 * page_size; >>>> @@ -1167,8 +1166,9 @@ int sanity_tests(void) >>>>       if (fmem == MAP_FAILED) >>>>           ksft_exit_fail_msg("error nomem %d %s\n", errno, >>>> strerror(errno)); >>>>   -    tmp_buf = malloc(sbuf.st_size); >>>> -    memcpy(tmp_buf, fmem, sbuf.st_size); >>>> +    /* Fault in every page by reading the first byte */ >>>> +    for (i = 0; i < sbuf.st_size; i += page_size) >>>> +        (void)*(volatile char *)(fmem + i); >>> >>> We have FORCE_READ() in vm_util.h for this. Perhaps that would be >>> better? >> >> Agreed, and if we have multiple patterns where we want to force_read a >> bigger area, maybe we should provide a helper for that? > > I've found just a couple of cases where FORCE_READ() is used for a > larger area (in hugetlb-madvise.c and split_huge_page_test.c). The step > size isn't the same in any of these cases though. We could have > something like fault_area(addr, size, step) but maybe the loops are > clear enough already? Note that even for hugtlb we can read page-per-page, no need to hugetlb-page-per-hugetlb-page. Not sure if the performance change would make any real performance difference in this testing code. -- Cheers David