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Thu, 17 Jul 2025 04:24:59 -0700 (PDT) From: wang lian To: akpm@linux-foundation.org, broonie@kernel.org, david@redhat.com, lorenzo.stoakes@oracle.com, sj@kernel.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: brauner@kernel.org, gkwang@linx-info.com, jannh@google.com, Liam.Howlett@oracle.com, lianux.mm@gmail.com, ludovico.zy.wu@gmail.com, p1ucky0923@gmail.com, richard.weiyang@gmail.com, ryncsn@gmail.com, shuah@kernel.org, vbabka@suse.cz, zijing.zhang@proton.me Subject: [PATCH 2/2] selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));" Date: Thu, 17 Jul 2025 19:24:07 +0800 Message-ID: <20250717112407.13507-3-lianux.mm@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250717112407.13507-1-lianux.mm@gmail.com> References: <20250717112407.13507-1-lianux.mm@gmail.com> 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 Content-Type: text/plain; charset="utf-8" Several mm selftests use the `asm volatile("" : "+r" (variable));` construct to force a read of a variable, preventing the compiler from optimizing away the memory access. This idiom is cryptic and duplicated across multiple test files. Following a suggestion from David[1], this patch refactors this common pattern into a FORCE_READ() macro [1] https://lore.kernel.org/lkml/4a3e0759-caa1-4cfa-bc3f-402593f1eee3@redha= t.com/ Signed-off-by: wang lian Reviewed-by: Lorenzo Stoakes Acked-by: David Hildenbrand --- tools/testing/selftests/mm/cow.c | 30 +++++++++---------- tools/testing/selftests/mm/hugetlb-madvise.c | 5 +--- tools/testing/selftests/mm/migration.c | 13 ++++---- tools/testing/selftests/mm/pagemap_ioctl.c | 4 +-- .../selftests/mm/split_huge_page_test.c | 4 +-- 5 files changed, 24 insertions(+), 32 deletions(-) diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/= cow.c index 788e82b00b75..d30625c18259 100644 --- a/tools/testing/selftests/mm/cow.c +++ b/tools/testing/selftests/mm/cow.c @@ -1534,7 +1534,7 @@ static void test_ro_fast_pin(char *mem, const char *s= mem, size_t size) =20 static void run_with_zeropage(non_anon_test_fn fn, const char *desc) { - char *mem, *smem, tmp; + char *mem, *smem; =20 log_test_start("%s ... with shared zeropage", desc); =20 @@ -1554,8 +1554,8 @@ static void run_with_zeropage(non_anon_test_fn fn, co= nst char *desc) } =20 /* Read from the page to populate the shared zeropage. */ - tmp =3D *mem + *smem; - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); + FORCE_READ(smem); =20 fn(mem, smem, pagesize); munmap: @@ -1566,7 +1566,7 @@ static void run_with_zeropage(non_anon_test_fn fn, co= nst char *desc) =20 static void run_with_huge_zeropage(non_anon_test_fn fn, const char *desc) { - char *mem, *smem, *mmap_mem, *mmap_smem, tmp; + char *mem, *smem, *mmap_mem, *mmap_smem; size_t mmap_size; int ret; =20 @@ -1617,8 +1617,8 @@ static void run_with_huge_zeropage(non_anon_test_fn f= n, const char *desc) * the first sub-page and test if we get another sub-page populated * automatically. */ - tmp =3D *mem + *smem; - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); + FORCE_READ(smem); if (!pagemap_is_populated(pagemap_fd, mem + pagesize) || !pagemap_is_populated(pagemap_fd, smem + pagesize)) { ksft_test_result_skip("Did not get THPs populated\n"); @@ -1634,7 +1634,7 @@ static void run_with_huge_zeropage(non_anon_test_fn f= n, const char *desc) =20 static void run_with_memfd(non_anon_test_fn fn, const char *desc) { - char *mem, *smem, tmp; + char *mem, *smem; int fd; =20 log_test_start("%s ... with memfd", desc); @@ -1668,8 +1668,8 @@ static void run_with_memfd(non_anon_test_fn fn, const= char *desc) } =20 /* Fault the page in. */ - tmp =3D *mem + *smem; - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); + FORCE_READ(smem); =20 fn(mem, smem, pagesize); munmap: @@ -1682,7 +1682,7 @@ static void run_with_memfd(non_anon_test_fn fn, const= char *desc) =20 static void run_with_tmpfile(non_anon_test_fn fn, const char *desc) { - char *mem, *smem, tmp; + char *mem, *smem; FILE *file; int fd; =20 @@ -1724,8 +1724,8 @@ static void run_with_tmpfile(non_anon_test_fn fn, con= st char *desc) } =20 /* Fault the page in. */ - tmp =3D *mem + *smem; - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); + FORCE_READ(smem); =20 fn(mem, smem, pagesize); munmap: @@ -1740,7 +1740,7 @@ static void run_with_memfd_hugetlb(non_anon_test_fn f= n, const char *desc, size_t hugetlbsize) { int flags =3D MFD_HUGETLB; - char *mem, *smem, tmp; + char *mem, *smem; int fd; =20 log_test_start("%s ... with memfd hugetlb (%zu kB)", desc, @@ -1778,8 +1778,8 @@ static void run_with_memfd_hugetlb(non_anon_test_fn f= n, const char *desc, } =20 /* Fault the page in. */ - tmp =3D *mem + *smem; - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); + FORCE_READ(smem); =20 fn(mem, smem, hugetlbsize); munmap: diff --git a/tools/testing/selftests/mm/hugetlb-madvise.c b/tools/testing/s= elftests/mm/hugetlb-madvise.c index e74107185324..1afe14b9dc0c 100644 --- a/tools/testing/selftests/mm/hugetlb-madvise.c +++ b/tools/testing/selftests/mm/hugetlb-madvise.c @@ -47,14 +47,11 @@ void write_fault_pages(void *addr, unsigned long nr_pag= es) =20 void read_fault_pages(void *addr, unsigned long nr_pages) { - volatile unsigned long dummy =3D 0; unsigned long i; =20 for (i =3D 0; i < nr_pages; i++) { - dummy +=3D *((unsigned long *)(addr + (i * huge_page_size))); - /* Prevent the compiler from optimizing out the entire loop: */ - asm volatile("" : "+r" (dummy)); + FORCE_READ(((unsigned long *)(addr + (i * huge_page_size)))); } } =20 diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftes= ts/mm/migration.c index a306f8bab087..c5a73617796a 100644 --- a/tools/testing/selftests/mm/migration.c +++ b/tools/testing/selftests/mm/migration.c @@ -16,6 +16,7 @@ #include #include #include +#include "vm_util.h" =20 #define TWOMEG (2<<20) #define RUNTIME (20) @@ -103,15 +104,13 @@ int migrate(uint64_t *ptr, int n1, int n2) =20 void *access_mem(void *ptr) { - volatile uint64_t y =3D 0; - volatile uint64_t *x =3D ptr; - while (1) { pthread_testcancel(); - y +=3D *x; - - /* Prevent the compiler from optimizing out the writes to y: */ - asm volatile("" : "+r" (y)); + /* Force a read from the memory pointed to by ptr. This ensures + * the memory access actually happens and prevents the compiler + * from optimizing away this entire loop. + */ + FORCE_READ((uint64_t *)ptr); } =20 return NULL; diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c b/tools/testing/sel= ftests/mm/pagemap_ioctl.c index c2dcda78ad31..0d4209eef0c3 100644 --- a/tools/testing/selftests/mm/pagemap_ioctl.c +++ b/tools/testing/selftests/mm/pagemap_ioctl.c @@ -1525,9 +1525,7 @@ void zeropfn_tests(void) =20 ret =3D madvise(mem, hpage_size, MADV_HUGEPAGE); if (!ret) { - char tmp =3D *mem; - - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); =20 ret =3D pagemap_ioctl(mem, hpage_size, &vec, 1, 0, 0, PAGE_IS_PFNZERO, 0, 0, PAGE_IS_PFNZERO); diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/test= ing/selftests/mm/split_huge_page_test.c index f0d9c035641d..05de1fc0005b 100644 --- a/tools/testing/selftests/mm/split_huge_page_test.c +++ b/tools/testing/selftests/mm/split_huge_page_test.c @@ -399,7 +399,6 @@ int create_pagecache_thp_and_fd(const char *testfile, s= ize_t fd_size, int *fd, char **addr) { size_t i; - int dummy =3D 0; unsigned char buf[1024]; =20 srand(time(NULL)); @@ -441,8 +440,7 @@ int create_pagecache_thp_and_fd(const char *testfile, s= ize_t fd_size, int *fd, madvise(*addr, fd_size, MADV_HUGEPAGE); =20 for (size_t i =3D 0; i < fd_size; i++) - dummy +=3D *(*addr + i); - asm volatile("" : "+r" (dummy)); + FORCE_READ((*addr + i)); =20 if (!check_huge_file(*addr, fd_size / pmd_pagesize, pmd_pagesize)) { ksft_print_msg("No large pagecache folio generated, please provide a fil= esystem supporting large folio\n"); --=20 2.43.0