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Wed, 16 Jul 2025 05:31:41 -0700 (PDT) Received: from DESKTOP-GIED850.localdomain ([114.247.113.178]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-31c9f1d3133sm1428607a91.4.2025.07.16.05.31.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Jul 2025 05:31:40 -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, jannh@google.com, Liam.Howlett@oracle.com, shuah@kernel.org, vbabka@suse.cz, ludovico.zy.wu@gmail.com, gkwang@linx-info.com, p1ucky0923@gmail.com, ryncsn@gmail.com, zijing.zhang@proton.me, lianux.mm@gmail.com Subject: [PATCH] selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));" Date: Wed, 16 Jul 2025 20:31:26 +0800 Message-ID: <20250716123126.3851-1-lianux.mm@gmail.com> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: B48044001A X-Rspamd-Server: rspam06 X-Stat-Signature: coipw9u4dugxx15e5xo7ntyzx8jxx3u8 X-HE-Tag: 1752669102-205656 X-HE-Meta: U2FsdGVkX1884379CCPovJ83qy71Yr/EJLBgx9InreOptJ5MlcD002OnfoF8J8mjemzMC9OjJap6Z1m9FlNBHgfcO3IG1Wi0T7tD7uPDuleCgvhMAXJMwYsUks9Zz4evdMLJqBzj55yztNjew0p5WnDCFIwXJujTKat1wYzNaw9xcSDszELobsa09qewx8egY+JVlAnLwZVvcHUb7BW6K8xToopjQxq7in9MtdtB14eT0C5N0gFQDDlXdUUFk4AzANiM8/lF9ScZEua2CDeA73ZibQL/D59f3GnHLfu/JJ6CdU0heLcu1cH/dTxQxK+GYLIlhG400Rs2knf1+UQIwbJoqZ2KOIL8u4vZvrEY+fZLAflWggXvd+2VJAAz5sjsmc+7h7n3kEumFOqOxSS5wJNx4IjNtfcsUoLv24WTpr8LyiWtKVD++oXUySLsyJ8JFKl//NWFsPSIczhPe9uxq5Op6pbh+dtPH7omij+ygDi4muNEIUHXSvrch65GiIGSWKogY3wJ/QHnhnEt9pwIM4ILABqQFI/VHZc8tjsbOgTloWWvRYmsGZtzKNrImcn7P/+RBPuPZ9VNeiQ0Ny4zjQ27H/qXTAeAuHhwWkxMLX/4RLtZP0Bw9lqKkwdMqbaIZaAkeXqY213QOWhui8nVt6Ys/wqSPMYDP8s94MBYwrhK0a1/HvEH3mxbPH63a5qGQUVeDfQrG6kDKmNUhRdxTr49pkYUrzDPq2OP361VQHfLnCUqmyz0lHMBwEgiQ5sNygWMqtLagcj40TxRtH55fotEpYDrBAe3CVxmqji4J2xhTbGVZ3VbP26cdSIk27LWXADxbggTrwS9Qr1h1e2yWvndNHjmBVG7WdZKqeIXQ3jjmVEYmjEMtUmco+e3v5v9+jjM9A92zzjhG5180LGqSqTBOLwsq1EKqt+NT89yeSA3jMBsvMj3Nn8Pz7tpncW/SzdsIHfS57ycxoIj1G8 5To0zDbb kLPqv5tQlA92pNnT9msK25utMEvwtP3pn3A8TfigAnV+w3xX6oi6qdWPyapfMy+MAvBgh+hFzsRdAF4OB0muQTHxLRmDxJMd4X/dJZVadfeK4yOoJBvsgWwvi6vBpTVztMRP2g/PFECer6H0n8oeYcPviMPXnJHP267KuNjQnwGpofuEWNVJylc89b79ucG928cfsx366730uTt8b77BIE3unPnb2H7tkiVJDy1GaaZncSpAAagLpuhee1xXsTuTngvab6rmbpqkGXUfKN58dbwqKKFUkqXikCorzDjiGNpVkr3omR3hSrpvgBJIKGg+fMKxsO0PyEk3ip0TGSF1nVBMTI5Q1BnzjyrAK6rSVhkjXlsB8h1akmOCuQOb0rEEFOLWtG3HgekBM6MYzeK8F5K9UbpyXDCye4hi+9tWYsqSOAL5VyQLMCk1NIUAk9LwUt64cezzet6L5RB62dceesqWtsRMuQiv0CkMSpMR/DpixNoAiXxM248Lcf5gdPQwgiWfmEGrKRh8iCc7yuvO05vm9PN/3lXeQDIsT6VihybmSCf/s9HSxH7xYE7jrQUf/ORInWisPiswq2wD2Suvf7OMxFQv6pucBpTTiN1xvDzfoacBhi7TTmliHW1iYRQetMODx X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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@redhat.com/ Signed-off-by: wang lian Reviewed-by: Lorenzo Stoakes --- 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 *smem, size_t size) static void run_with_zeropage(non_anon_test_fn fn, const char *desc) { - char *mem, *smem, tmp; + char *mem, *smem; log_test_start("%s ... with shared zeropage", desc); @@ -1554,8 +1554,8 @@ static void run_with_zeropage(non_anon_test_fn fn, const char *desc) } /* Read from the page to populate the shared zeropage. */ - tmp = *mem + *smem; - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); + FORCE_READ(smem); fn(mem, smem, pagesize); munmap: @@ -1566,7 +1566,7 @@ static void run_with_zeropage(non_anon_test_fn fn, const char *desc) 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; @@ -1617,8 +1617,8 @@ static void run_with_huge_zeropage(non_anon_test_fn fn, const char *desc) * the first sub-page and test if we get another sub-page populated * automatically. */ - tmp = *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 fn, const char *desc) static void run_with_memfd(non_anon_test_fn fn, const char *desc) { - char *mem, *smem, tmp; + char *mem, *smem; int fd; log_test_start("%s ... with memfd", desc); @@ -1668,8 +1668,8 @@ static void run_with_memfd(non_anon_test_fn fn, const char *desc) } /* Fault the page in. */ - tmp = *mem + *smem; - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); + FORCE_READ(smem); fn(mem, smem, pagesize); munmap: @@ -1682,7 +1682,7 @@ static void run_with_memfd(non_anon_test_fn fn, const char *desc) static void run_with_tmpfile(non_anon_test_fn fn, const char *desc) { - char *mem, *smem, tmp; + char *mem, *smem; FILE *file; int fd; @@ -1724,8 +1724,8 @@ static void run_with_tmpfile(non_anon_test_fn fn, const char *desc) } /* Fault the page in. */ - tmp = *mem + *smem; - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); + FORCE_READ(smem); fn(mem, smem, pagesize); munmap: @@ -1740,7 +1740,7 @@ static void run_with_memfd_hugetlb(non_anon_test_fn fn, const char *desc, size_t hugetlbsize) { int flags = MFD_HUGETLB; - char *mem, *smem, tmp; + char *mem, *smem; int fd; log_test_start("%s ... with memfd hugetlb (%zu kB)", desc, @@ -1778,8 +1778,8 @@ static void run_with_memfd_hugetlb(non_anon_test_fn fn, const char *desc, } /* Fault the page in. */ - tmp = *mem + *smem; - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); + FORCE_READ(smem); fn(mem, smem, hugetlbsize); munmap: diff --git a/tools/testing/selftests/mm/hugetlb-madvise.c b/tools/testing/selftests/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_pages) void read_fault_pages(void *addr, unsigned long nr_pages) { - volatile unsigned long dummy = 0; unsigned long i; for (i = 0; i < nr_pages; i++) { - dummy += *((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)))); } } diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftests/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" #define TWOMEG (2<<20) #define RUNTIME (20) @@ -103,15 +104,13 @@ int migrate(uint64_t *ptr, int n1, int n2) void *access_mem(void *ptr) { - volatile uint64_t y = 0; - volatile uint64_t *x = ptr; - while (1) { pthread_testcancel(); - y += *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); } return NULL; diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c b/tools/testing/selftests/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) ret = madvise(mem, hpage_size, MADV_HUGEPAGE); if (!ret) { - char tmp = *mem; - - asm volatile("" : "+r" (tmp)); + FORCE_READ(mem); ret = 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/testing/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, size_t fd_size, int *fd, char **addr) { size_t i; - int dummy = 0; unsigned char buf[1024]; srand(time(NULL)); @@ -441,8 +440,7 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd, madvise(*addr, fd_size, MADV_HUGEPAGE); for (size_t i = 0; i < fd_size; i++) - dummy += *(*addr + i); - asm volatile("" : "+r" (dummy)); + FORCE_READ((*addr + i)); 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"); -- 2.43.0