selftests/mm: khugepaged: initialize file contents via mmap

file_setup_area() currently allocates anonymous memory, fills it, and
writes it into the backing file used for collapse testing.

Instead of copying data through write(), resize the file with ftruncate(),
map it directly with MAP_SHARED, and initialize the mapped area in place.

This simplifies the setup path and avoids the need for explicit partial
write handling.

Link: https://lore.kernel.org/20260429115816.98824-1-agarwal.vineet2006@gmail.com
Signed-off-by: Vineet Agarwal <agarwal.vineet2006@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 3fe7ef04ac62efdf61388c330a4ce82c705b0127..c8393ca52cab73d370454d284ee75a9f5e645f30 100644 (file)
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -373,7 +373,7 @@ static void *file_setup_area(int nr_hpages)
        unlink(finfo.path);  /* Cleanup from previous failed tests */
        printf("Creating %s for collapse%s...", finfo.path,
               finfo.type == VMA_SHMEM ? " (tmpfs)" : "");
-       fd = open(finfo.path, O_DSYNC | O_CREAT | O_RDWR | O_TRUNC | O_EXCL,
+       fd = open(finfo.path, O_CREAT | O_RDWR | O_TRUNC | O_EXCL,
                  777);
        if (fd < 0) {
                perror("open()");
@@ -381,9 +381,21 @@ static void *file_setup_area(int nr_hpages)
        }
 
        size = nr_hpages * hpage_pmd_size;
-       p = alloc_mapping(nr_hpages);
+       if (ftruncate(fd, size)) {
+               perror("ftruncate()");
+               exit(EXIT_FAILURE);
+       }
+       p = mmap(BASE_ADDR, size, PROT_READ | PROT_WRITE,
+               MAP_SHARED, fd, 0);
+       if (p != BASE_ADDR) {
+               perror("mmap()");
+               exit(EXIT_FAILURE);
+       }
        fill_memory(p, 0, size);
-       write(fd, p, size);
+       if (msync(p, size, MS_SYNC)) {
+               perror("msync()");
+               exit(EXIT_FAILURE);
+       }
        close(fd);
        munmap(p, size);
        success("OK");