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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: 5nsrfwrk5zsjgwkffu9s1tdyxpdfrfee X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 1433C1A0003 X-HE-Tag: 1766063921-913667 X-HE-Meta: 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 lDTs4hVo kRa071Z5nODmrh6ulClCQ1Thdl5J3JDwo3Dl9Bae7d4XvDQTLHd09VF+XK12E8HfQ238lMS10ywdvL/mQ/MY8af12Ahcqupbm38U8U1qxkx6RB74bnzgINP8tvyICMpWOdNzKs2o3q9crYjDHMWgYQaNisAdkTduH7G6f1o9P/8+hPvwX2h0Mke0dB3u4g0IbUIIPXw8adOXYVT76I0GZdLLzE87CKHyELIXskvTa8paIAdbniE4U3xv/b51PxZnER2zfFBV+7NF7PdKICcgtszsFXw== 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: 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? - Kevin