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 1963A2FF66A; Mon, 19 Jan 2026 10:55:58 +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=1768820159; cv=none; b=Z71M+26Hl3Pke5Iht/xUOtV086jZ8vrc+qxnUWiLNZAnedoPZ1rYrt2TMgxshUFAWhnEx2wuxKD91Q5TRqn/YVWxlqBaUS5mdVla102nWp5WvvmPfINO8qfkqn73Qjh2CASrU6VKCskChAFX1tpFmdCwEWj5VeGQ7wvYG308YcE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768820159; c=relaxed/simple; bh=bsXo26KZ+K1aH/HZ8wolPUoG9a2d4fNHkR3P0zLa+8g=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eUSPb8n+ee3CKsQSDyHacUg/LlgphD7W82pLp3vi1udnnRa9QPVN1m9/OE18bql9CLrCebzG2E8lbtmsyDS1bc208fc8zUOMpyUEUBeEDwYJAp/MfQUkS+bD8anba5ZrC09eADtcqyHhcj6EY1KrDL7dHPy5qO7AwypCIMPwmD8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=U5HR1K7C; 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="U5HR1K7C" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7F7E2C116C6; Mon, 19 Jan 2026 10:55:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768820158; bh=bsXo26KZ+K1aH/HZ8wolPUoG9a2d4fNHkR3P0zLa+8g=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=U5HR1K7Cjv0Cp+7YA9y3rZzYh3llbIkfZP8dDEoV9I93qC40yuDZuPbkDtUVAE8Xg W7/u0Dc4zylWNGHI2B/csqj7mS8kuwdP6elJFVLdx6UbEdH6hy7LNPodk4rb2UvPku PRsyafmBOay1dqnXvPNE9mACu05Ir5P33XWVzP8Bc91mrb8vmXgUkQqrGf1DRxq/Nb 9MdLKrAaR2r//UIh9a4FhU6Nq64ghVu9kwpROwSidCRdJtB2M2Xbz/SlUJqMImyGP4 ouTywClMcWbwMw59omh7dCa2luVHaowpKS6lyNbYgozqnWikaAZQprzz+3UpK3ecTj yUcKnCrZxwa4g== Message-ID: Date: Mon, 19 Jan 2026 11:55:54 +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 v2 5/8] selftests/mm: introduce helper to read every page in range To: Kevin Brodsky , linux-mm@kvack.org, linux-kselftest@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Mark Brown , Ryan Roberts , Shuah Khan References: <20260107164842.3289559-1-kevin.brodsky@arm.com> <20260107164842.3289559-6-kevin.brodsky@arm.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/7/26 17:48, Kevin Brodsky wrote: > FORCE_READ(*addr) ensures that the compiler will emit a load from > addr. Several tests need to trigger such a load for every page in > the range [addr, addr + len), ensuring that every page is faulted > in, if it wasn't already. > > Introduce a new helper force_read_pages_in_range() that does exactly > that and replace existing loops with a call to it. Some of those > loops have a different step size, but reading from every page is > appropriate in all cases. > > Signed-off-by: Kevin Brodsky > --- > tools/testing/selftests/mm/hugetlb-madvise.c | 9 +-------- > tools/testing/selftests/mm/pfnmap.c | 16 ++++++---------- > .../testing/selftests/mm/split_huge_page_test.c | 6 +----- > tools/testing/selftests/mm/vm_util.h | 6 ++++++ > 4 files changed, 14 insertions(+), 23 deletions(-) > > diff --git a/tools/testing/selftests/mm/hugetlb-madvise.c b/tools/testing/selftests/mm/hugetlb-madvise.c > index 05d9d2805ae4..1f82568ae262 100644 > --- a/tools/testing/selftests/mm/hugetlb-madvise.c > +++ b/tools/testing/selftests/mm/hugetlb-madvise.c > @@ -47,14 +47,7 @@ void write_fault_pages(void *addr, unsigned long nr_pages) > > void read_fault_pages(void *addr, unsigned long nr_pages) > { > - unsigned long i; > - > - for (i = 0; i < nr_pages; i++) { > - unsigned long *addr2 = > - ((unsigned long *)(addr + (i * huge_page_size))); > - /* Prevent the compiler from optimizing out the entire loop: */ > - FORCE_READ(*addr2); > - } > + force_read_pages_in_range(addr, nr_pages * huge_page_size); > } > > int main(int argc, char **argv) > diff --git a/tools/testing/selftests/mm/pfnmap.c b/tools/testing/selftests/mm/pfnmap.c > index f546dfb10cae..35b0e3ed54cd 100644 > --- a/tools/testing/selftests/mm/pfnmap.c > +++ b/tools/testing/selftests/mm/pfnmap.c > @@ -33,20 +33,17 @@ static void signal_handler(int sig) > siglongjmp(sigjmp_buf_env, -EFAULT); > } > > -static int test_read_access(char *addr, size_t size, size_t pagesize) > +static int test_read_access(char *addr, size_t size) > { > - size_t offs; > int ret; > > if (signal(SIGSEGV, signal_handler) == SIG_ERR) > return -EINVAL; > > ret = sigsetjmp(sigjmp_buf_env, 1); > - if (!ret) { > - for (offs = 0; offs < size; offs += pagesize) > - /* Force a read that the compiler cannot optimize out. */ > - *((volatile char *)(addr + offs)); > - } > + if (!ret) > + force_read_pages_in_range(addr, size); > + > if (signal(SIGSEGV, SIG_DFL) == SIG_ERR) > return -EINVAL; > > @@ -138,7 +135,7 @@ FIXTURE_SETUP(pfnmap) > SKIP(return, "Invalid file: '%s'. Not pfnmap'ed\n", file); > > /* ... and want to be able to read from them. */ > - if (test_read_access(self->addr1, self->size1, self->pagesize)) > + if (test_read_access(self->addr1, self->size1)) > SKIP(return, "Cannot read-access mmap'ed '%s'\n", file); > > self->size2 = 0; > @@ -243,8 +240,7 @@ TEST_F(pfnmap, fork) > ASSERT_GE(pid, 0); > > if (!pid) { > - EXPECT_EQ(test_read_access(self->addr1, self->size1, > - self->pagesize), 0); > + EXPECT_EQ(test_read_access(self->addr1, self->size1), 0); > exit(0); > } > > diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c > index 40799f3f0213..65a89ceca4a5 100644 > --- a/tools/testing/selftests/mm/split_huge_page_test.c > +++ b/tools/testing/selftests/mm/split_huge_page_test.c > @@ -652,11 +652,7 @@ static int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, > } > madvise(*addr, fd_size, MADV_HUGEPAGE); > > - for (size_t i = 0; i < fd_size; i++) { > - char *addr2 = *addr + i; > - > - FORCE_READ(*addr2); > - } > + force_read_pages_in_range(*addr, fd_size); > > if (!check_huge_file(*addr, fd_size / pmd_pagesize, pmd_pagesize)) { > ksft_print_msg("No large pagecache folio generated, please provide a filesystem supporting large folio\n"); > diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h > index 6ad32b1830f1..74bdf96161d7 100644 > --- a/tools/testing/selftests/mm/vm_util.h > +++ b/tools/testing/selftests/mm/vm_util.h > @@ -54,6 +54,12 @@ static inline unsigned int pshift(void) > return __page_shift; > } > > +static inline void force_read_pages_in_range(char *addr, size_t len) > +{ > + for (size_t i = 0; i < len; i += psize()) > + FORCE_READ(addr[i]); > +} > + Of course, we could also just pass the pagesize static inline void force_read_pages_in_range(char *addr, size_t len, size_t pagesize) { for (size_t i = 0; i < len; i += pagesize) FORCE_READ(addr[i]); } Or alternatively even better: static inline void force_read_pages(char *addr, unsigned int nr_pages, size_t pagesize) { for (size_t i = 0; i < nr_pages; i++) FORCE_READ(addr[i * pagesize]); } Then there is no change at all and we avoid the repeated psize() naturally. Thoughts? -- Cheers David