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<div class="moz-cite-prefix">On 27/03/26 12:45, Sayali Patil wrote:<br>
</div>
<blockquote type="cite"
cite="mid:2fd965ce641d32a759984943a427fde47d7c3b13.1774591179.git.sayalip@linux.ibm.com">
<pre wrap="" class="moz-quote-pre">The split_file_backed_thp() test mounts a tmpfs with a fixed size of
"4m". This works on systems with smaller PMD page sizes,
but fails on configurations where the PMD huge page size is
larger (e.g. 16MB).
On such systems, the fixed 4MB tmpfs is insufficient to allocate even
a single PMD-sized THP, causing the test to fail.
Fix this by sizing the tmpfs dynamically based on the runtime
pmd_pagesize, allocating space for two PMD-sized pages.
Before patch:
running ./split_huge_page_test /tmp/xfs_dir_YTrI5E
--------------------------------------------------
TAP version 13
1..55
ok 1 Split zero filled huge pages successful
ok 2 Split huge pages to order 0 successful
ok 3 Split huge pages to order 2 successful
ok 4 Split huge pages to order 3 successful
ok 5 Split huge pages to order 4 successful
ok 6 Split huge pages to order 5 successful
ok 7 Split huge pages to order 6 successful
ok 8 Split huge pages to order 7 successful
ok 9 Split PTE-mapped huge pages successful
Please enable pr_debug in split_huge_pages_in_file() for more info.
Failed to write data to testing file: Success (0)
Bail out! Error occurred
Planned tests != run tests (55 != 9)
Totals: pass:9 fail:0 xfail:0 xpass:0 skip:0 error:0
[FAIL]
After patch:
--------------------------------------------------
running ./split_huge_page_test /tmp/xfs_dir_bMvj6o
--------------------------------------------------
TAP version 13
1..55
ok 1 Split zero filled huge pages successful
ok 2 Split huge pages to order 0 successful
ok 3 Split huge pages to order 2 successful
ok 4 Split huge pages to order 3 successful
ok 5 Split huge pages to order 4 successful
ok 6 Split huge pages to order 5 successful
ok 7 Split huge pages to order 6 successful
ok 8 Split huge pages to order 7 successful
ok 9 Split PTE-mapped huge pages successful
Please enable pr_debug in split_huge_pages_in_file() for more info.
Please check dmesg for more information
ok 10 File-backed THP split to order 0 test done
Please enable pr_debug in split_huge_pages_in_file() for more info.
Please check dmesg for more information
ok 11 File-backed THP split to order 1 test done
Please enable pr_debug in split_huge_pages_in_file() for more info.
Please check dmesg for more information
ok 12 File-backed THP split to order 2 test done
...
ok 55 Split PMD-mapped pagecache folio to order 7 at
in-folio offset 128 passed
Totals: pass:55 fail:0 xfail:0 xpass:0 skip:0 error:0
[PASS]
ok 1 split_huge_page_test /tmp/xfs_dir_bMvj6o
Fixes: fbe37501b252 ("mm: huge_memory: debugfs for file-backed THP split")
Reviewed-by: Zi Yan <a class="moz-txt-link-rfc2396E" href="mailto:ziy@nvidia.com"><ziy@nvidia.com></a>
Reviewed-by: David Hildenbrand (Arm) <a class="moz-txt-link-rfc2396E" href="mailto:david@kernel.org"><david@kernel.org></a>
Tested-by: Venkat Rao Bagalkote <a class="moz-txt-link-rfc2396E" href="mailto:venkat88@linux.ibm.com"><venkat88@linux.ibm.com></a>
Signed-off-by: Sayali Patil <a class="moz-txt-link-rfc2396E" href="mailto:sayalip@linux.ibm.com"><sayalip@linux.ibm.com></a>
---
tools/testing/selftests/mm/split_huge_page_test.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index e0167111bdd1..57e8a1c9647a 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -484,6 +484,8 @@ static void split_file_backed_thp(int order)
char tmpfs_template[] = "/tmp/thp_split_XXXXXX";
const char *tmpfs_loc = mkdtemp(tmpfs_template);
char testfile[INPUT_MAX];
+ unsigned long size = 2 * pmd_pagesize;
+ char opts[64];
ssize_t num_written, num_read;
char *file_buf1, *file_buf2;
uint64_t pgoff_start = 0, pgoff_end = 1024;
@@ -503,7 +505,8 @@ static void split_file_backed_thp(int order)
file_buf1[i] = (char)i;
memset(file_buf2, 0, pmd_pagesize);
- status = mount("tmpfs", tmpfs_loc, "tmpfs", 0, "huge=always,size=4m");
+ snprintf(opts, sizeof(opts), "huge=always,size=%lu", size);
+ status = mount("tmpfs", tmpfs_loc, "tmpfs", 0, opts);
if (status)
ksft_exit_fail_msg("Unable to create a tmpfs for testing\n");</pre>
</blockquote>
<font face="monospace">AI review question:</font>
<blockquote type="cite"
cite="mid:2fd965ce641d32a759984943a427fde47d7c3b13.1774591179.git.sayalip@linux.ibm.com">
<pre wrap="" class="moz-quote-pre">Are file_buf1 and file_buf2 being leaked here?
While reviewing the patch's changes to support larger PMD sizes, I noticed
that earlier in this function file_buf1 and file_buf2 are dynamically
allocated using pmd_pagesize:
file_buf1 = (char *)malloc(pmd_pagesize);
file_buf2 = (char *)malloc(pmd_pagesize);
Looking at the end of the function, the success path returns without freeing
either buffer:
ksft_print_msg("Please check dmesg for more information\n");
ksft_test_result_pass("File-backed THP split to order %d test done\n", order);
return;
Since this function is called in a loop for each split order, could this
cause a significant memory leak? On architectures with large PMD sizes
(like arm64 with 64KB base pages, where the PMD size is 512MB), leaking
these buffers repeatedly could exhaust system memory and trigger the OOM
killer during the test run.
</pre>
<br>
</blockquote>
<font face="monospace">Yes, both file_buf1 and file_buf2 are leaked
on the success path and </font><br>
<font face="monospace">some failure paths.</font><font
face="monospace"> </font><br>
<font face="monospace">Since this function is invoked in a loop for
each split order, the leak accumulates over time. </font><br>
<font face="monospace">On systems with large PMD sizes, this can
potentially trigger OOM during the test run.</font><br>
<br>
<font face="monospace">This was likely not noticeable earlier with
smaller PMD sizes, but becomes significant </font><br>
<font face="monospace">with larger configurations.</font><br>
<font face="monospace">This appears to be a pre-existing issue and
not introduced by my patch.</font><br>
<font face="monospace">
I will prepare a separate fix to free both buffers on all exit
paths to</font><br>
<font face="monospace">prevent this memory leak.</font><br>
<br>
<font face="monospace">Thanks,<br>
Sayali</font><br>
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