From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 6F5D331D36B; Mon, 19 Jan 2026 13:29:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768829368; cv=none; b=WsZgPjOz4OJbOI56ExTdmVk7Rwfk252jJfdZ4w3m09e1eadNSbvp99EKAoYc9jfEmeB9289Lxaiyflmr9ldWvkBQ/8JPV/BBAAK93OrIxDlarL85zZCnzhjHY7Y8/BHvJbZnmUD2ow/08dEoBvk9lvpjV1b/os5vqOjcT7bMUl0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768829368; c=relaxed/simple; bh=8v8ZMpGbwFG1Br1hfdCEyTZrMXw9YgADFPAcQwGpm44=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LIZfGBboCoK9fZfUSK7PPrqokYxHfe6fNw2kk/ZaaEwF8VrCGoUCQ1FI1S3d/AhH0BVPeA2lPTrmzXSNo4xAgPv0zdTD17RGzzvdmTeecqTbet+YuwWHdm/OV0J/IkS9Ju20xYNlnNmRGoYjCKjXK4eXuPan0yg61xDQegnBkgk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 349CD497; Mon, 19 Jan 2026 05:29:19 -0800 (PST) Received: from [10.44.160.85] (e126510-lin.lund.arm.com [10.44.160.85]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 316413F740; Mon, 19 Jan 2026 05:29:23 -0800 (PST) Message-ID: <5660b5ea-16f7-485a-8daa-d3d6cb4af310@arm.com> Date: Mon, 19 Jan 2026 14:29:21 +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: "David Hildenbrand (Red Hat)" , 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: Kevin Brodsky Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 19/01/2026 11:55, David Hildenbrand (Red Hat) wrote: > 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? Sure we can do that. I concluded that all tests fetch the pagesize in a different way and some aren't using psize() sparingly either (e.g. gup_test) but I suppose that avoiding some ugliness doesn't hurt :) Of course this especially makes sense for the hugepage tests (then we can still read hugepage by hugepage). - Kevin