[PATCH 3/3] selftests/mm: virtual_address_range: Dump to /dev/null

[Thomas Weißschuh]

During the execution of validate_complete_va_space() a lot of memory is
on the VM subsystem. When running on a low memory subsystem an OOM may
be triggered, when writing to the dump file as the filesystem may also
require memory.

On my test system with 1100MiB physical memory:

        Tasks state (memory values in pages):
        [  pid  ]   uid  tgid total_vm      rss rss_anon rss_file rss_shmem 
pgtables_bytes swapents oom_score_adj name
        [     57]     0    57 34359215953      695      256        0       439 
1064390656        0             0 virtual_address

        Out of memory: Killed process 57 (virtual_address) 
total-vm:137436863812kB, anon-rss:1024kB, file-rss:0kB, shmem-rss:1756kB, UID:0 
pgtables:1039444kB oom_score_adj:0
        <snip>
        fault_in_iov_iter_readable+0x4a/0xd0
        generic_perform_write+0x9c/0x280
        shmem_file_write_iter+0x86/0x90
        vfs_write+0x29c/0x480
        ksys_write+0x6c/0xe0
        do_syscall_64+0x9e/0x1a0
        entry_SYSCALL_64_after_hwframe+0x77/0x7f

Write the dumped data into /dev/null instead which does not require
additional memory during write(), making the code simpler as a
side-effect.

Signed-off-by: Thomas Weißschuh <thomas.weisssc...@linutronix.de>
---
 tools/testing/selftests/mm/virtual_address_range.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/mm/virtual_address_range.c 
b/tools/testing/selftests/mm/virtual_address_range.c
index 
484f82c7b7c871f82a7d9ec6d6c649f2ab1eb0cd..4042fd878acd702d23da2c3293292de33bd48143
 100644
--- a/tools/testing/selftests/mm/virtual_address_range.c
+++ b/tools/testing/selftests/mm/virtual_address_range.c
@@ -103,10 +103,9 @@ static int validate_complete_va_space(void)
        FILE *file;
        int fd;
 
-       fd = open("va_dump", O_CREAT | O_WRONLY, 0600);
-       unlink("va_dump");
+       fd = open("/dev/null", O_WRONLY);
        if (fd < 0) {
-               ksft_test_result_skip("cannot create or open dump file\n");
+               ksft_test_result_skip("cannot create or open /dev/null\n");
                ksft_finished();
        }
 
@@ -152,7 +151,6 @@ static int validate_complete_va_space(void)
                while (start_addr + hop < end_addr) {
                        if (write(fd, (void *)(start_addr + hop), 1) != 1)
                                return 1;
-                       lseek(fd, 0, SEEK_SET);
 
                        hop += MAP_CHUNK_SIZE;
                }

-- 
2.47.1