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selftests/mm: simplify byte pattern checking in mremap_test

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The original version of mremap_test (7df666253f26: "kselftests: vm: add
mremap tests") validated remapped contents byte-by-byte and printed a
mismatch index in case the bytes streams didn't match.  That was rather
inefficient, especially also if the test passed.

Later, commit 7033c6cc96 ("selftests/mm: mremap_test: optimize execution
time from minutes to seconds using chunkwise memcmp") used memcmp() on
bigger chunks, to fallback to byte-wise scanning to detect the problematic
index only if it discovered a problem.

However, the implementation is overly complicated (e.g., get_sqrt() is
currently not optimal) and we don't really have to report the exact index:
whoever debugs the failing test can figure that out.

Let's simplify by just comparing both byte streams with memcmp() and not
detecting the exact failed index.

Link: https://lore.kernel.org/20260415044509.579428-1-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Reported-by: Sarthak Sharma <sarthak.sharma@arm.com>
Tested-by: Sarthak Sharma <sarthak.sharma@arm.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.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>
Cc: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Dev Jain 2026-04-15 10:15:09 +05:30 committed by Andrew Morton
parent 8aa442cfce
commit 7e8983f317
1 changed files with 10 additions and 99 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

109
tools/testing/selftests/mm/mremap_test.c
View File

@ -76,27 +76,6 @@ enum {
.expect_failure = should_fail \
}
/* compute square root using binary search */
static unsigned long get_sqrt(unsigned long val)
{
unsigned long low = 1;
/* assuming rand_size is less than 1TB */
unsigned long high = (1UL << 20);
while (low <= high) {
unsigned long mid = low + (high - low) / 2;
unsigned long temp = mid * mid;
if (temp == val)
return mid;
if (temp < val)
low = mid + 1;
high = mid - 1;
}
return low;
}
/*
* Returns false if the requested remap region overlaps with an
* existing mapping (e.g text, stack) else returns true.
@ -995,11 +974,9 @@ static long long remap_region(struct config c, unsigned int threshold_mb,
char *rand_addr)
{
void *addr, *tmp_addr, *src_addr, *dest_addr, *dest_preamble_addr = NULL;
unsigned long long t, d;
struct timespec t_start = {0, 0}, t_end = {0, 0};
long long start_ns, end_ns, align_mask, ret, offset;
unsigned long long threshold;
unsigned long num_chunks;
if (threshold_mb == VALIDATION_NO_THRESHOLD)
threshold = c.region_size;
@ -1068,87 +1045,21 @@ static long long remap_region(struct config c, unsigned int threshold_mb,
goto clean_up_dest_preamble;
}
/*
* Verify byte pattern after remapping. Employ an algorithm with a
* square root time complexity in threshold: divide the range into
* chunks, if memcmp() returns non-zero, only then perform an
* iteration in that chunk to find the mismatch index.
*/
num_chunks = get_sqrt(threshold);
for (unsigned long i = 0; i < num_chunks; ++i) {
size_t chunk_size = threshold / num_chunks;
unsigned long shift = i * chunk_size;
if (!memcmp(dest_addr + shift, rand_addr + shift, chunk_size))
continue;
/* brute force iteration only over mismatch segment */
for (t = shift; t < shift + chunk_size; ++t) {
if (((char *) dest_addr)[t] != rand_addr[t]) {
ksft_print_msg("Data after remap doesn't match at offset %llu\n",
t);
ksft_print_msg("Expected: %#x\t Got: %#x\n", rand_addr[t] & 0xff,
((char *) dest_addr)[t] & 0xff);
ret = -1;
goto clean_up_dest;
}
}
}
/*
* if threshold is not divisible by num_chunks, then check the
* last chunk
*/
for (t = num_chunks * (threshold / num_chunks); t < threshold; ++t) {
if (((char *) dest_addr)[t] != rand_addr[t]) {
ksft_print_msg("Data after remap doesn't match at offset %llu\n",
t);
ksft_print_msg("Expected: %#x\t Got: %#x\n", rand_addr[t] & 0xff,
((char *) dest_addr)[t] & 0xff);
ret = -1;
goto clean_up_dest;
}
/* Verify byte pattern after remapping */
if (memcmp(dest_addr, rand_addr, threshold)) {
ksft_print_msg("Data after remap doesn't match\n");
ret = -1;
goto clean_up_dest;
}
/* Verify the dest preamble byte pattern after remapping */
if (!c.dest_preamble_size)
goto no_preamble;
num_chunks = get_sqrt(c.dest_preamble_size);
for (unsigned long i = 0; i < num_chunks; ++i) {
size_t chunk_size = c.dest_preamble_size / num_chunks;
unsigned long shift = i * chunk_size;
if (!memcmp(dest_preamble_addr + shift, rand_addr + shift,
chunk_size))
continue;
/* brute force iteration only over mismatched segment */
for (d = shift; d < shift + chunk_size; ++d) {
if (((char *) dest_preamble_addr)[d] != rand_addr[d]) {
ksft_print_msg("Preamble data after remap doesn't match at offset %llu\n",
d);
ksft_print_msg("Expected: %#x\t Got: %#x\n", rand_addr[d] & 0xff,
((char *) dest_preamble_addr)[d] & 0xff);
ret = -1;
goto clean_up_dest;
}
}
if (c.dest_preamble_size &&
memcmp(dest_preamble_addr, rand_addr, c.dest_preamble_size)) {
ksft_print_msg("Preamble data after remap doesn't match\n");
ret = -1;
goto clean_up_dest;
}
for (d = num_chunks * (c.dest_preamble_size / num_chunks); d < c.dest_preamble_size; ++d) {
if (((char *) dest_preamble_addr)[d] != rand_addr[d]) {
ksft_print_msg("Preamble data after remap doesn't match at offset %llu\n",
d);
ksft_print_msg("Expected: %#x\t Got: %#x\n", rand_addr[d] & 0xff,
((char *) dest_preamble_addr)[d] & 0xff);
ret = -1;
goto clean_up_dest;
}
}
no_preamble:
start_ns = t_start.tv_sec * NS_PER_SEC + t_start.tv_nsec;
end_ns = t_end.tv_sec * NS_PER_SEC + t_end.tv_nsec;
ret = end_ns - start_ns;