Re: [PATCH v3 11/13] selftests/mm: fix double increment in linked list cleanup in compaction_test

[Sayali Patil]

On 27/03/26 12:46, Sayali Patil wrote:
> The cleanup loop of allocated memory currently uses:
>
>      for (entry = list; entry != NULL; entry = entry->next) {
>          munmap(entry->map, MAP_SIZE);
>          if (!entry->next)
>              break;
>          entry = entry->next;
>      }
>
> The inner entry = entry->next causes the loop to skip every
> other node, resulting in only half of the mapped regions being
> unmapped.
>
> Remove the redundant increment to ensure every entry is visited
> and unmapped during cleanup.
>
> Fixes: bd67d5c15cc1 ("Test compaction of mlocked memory")
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
> Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Tested-by: Venkat Rao Bagalkote <venkat88@xxxxxxxxxxxxx>
> Signed-off-by: Sayali Patil <sayalip@xxxxxxxxxxxxx>
> ---
>   tools/testing/selftests/mm/compaction_test.c | 3 ---
>   1 file changed, 3 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/compaction_test.c b/tools/testing/selftests/mm/compaction_test.c
> index 30209c40b697..f73930706bd0 100644
> --- a/tools/testing/selftests/mm/compaction_test.c
> +++ b/tools/testing/selftests/mm/compaction_test.c
> @@ -263,9 +263,6 @@ int main(int argc, char **argv)
>   
>   	for (entry = list; entry != NULL; entry = entry->next) {
>   		munmap(entry->map, MAP_SIZE);
> -		if (!entry->next)
> -			break;
> -		entry = entry->next;
>   	}
>   
>   	if (check_compaction(mem_free, hugepage_size,

Sorry, this change is not valid.

The goal of this test is to verify the kernel’s ability to compact
unevictable (MAP_LOCKED) pages. The loop is intentionally written to
unmap every other chunk, thereby creating fragmentation with locked pages
before check_compaction() is invoked.

With the proposed change (removing the double increment), the loop ends up
unmapping all allocated locked pages instead of leaving a fragmented
pattern. This results in memory being effectively unfragmented.

I will send v4 without this patch.

Thanks,
Sayali