Re: [PATCH v5 4/7] selftests: mm: Add a test for mutually aligned moves > PMD size

[Lorenzo Stoakes <lstoakes@gmail.com>]

On Tue, Aug 22, 2023 at 01:54:57AM +0000, Joel Fernandes (Google) wrote:
> This patch adds a test case to check if a PMD-alignment optimization
> successfully happens.
>
> I add support to make sure there is some room before the source mapping,
> otherwise the optimization to trigger PMD-aligned move will be disabled
> as the kernel will detect that a mapping before the source exists and
> such optimization becomes impossible.
>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
>  tools/testing/selftests/mm/mremap_test.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/mm/mremap_test.c b/tools/testing/selftests/mm/mremap_test.c
> index 6822d657f589..6304eb0947a3 100644
> --- a/tools/testing/selftests/mm/mremap_test.c
> +++ b/tools/testing/selftests/mm/mremap_test.c
> @@ -44,6 +44,7 @@ enum {
>  	_1MB = 1ULL << 20,
>  	_2MB = 2ULL << 20,
>  	_4MB = 4ULL << 20,
> +	_5MB = 5ULL << 20,
>  	_1GB = 1ULL << 30,
>  	_2GB = 2ULL << 30,
>  	PMD = _2MB,
> @@ -235,6 +236,11 @@ static void *get_source_mapping(struct config c)
>  	unsigned long long mmap_min_addr;
>
>  	mmap_min_addr = get_mmap_min_addr();
> +	/*
> +	 * For some tests, we need to not have any mappings below the
> +	 * source mapping. Add some headroom to mmap_min_addr for this.
> +	 */
> +	mmap_min_addr += 10 * _4MB;

To be super nitty, you _in theory_ can't necessarily rely on arbitrary VAs
being available even ones at a location that is the very opposite of where
mappings will go by default.

I guess the _ideal_ solution would be to PROT_NONE map a range to ensure
it's there then munmap() bits you don't want to exist, but that'd involve
reworking this whole test and yeah, not worth it.

>
>  retry:
>  	addr += c.src_alignment;
> @@ -434,7 +440,7 @@ static int parse_args(int argc, char **argv, unsigned int *threshold_mb,
>  	return 0;
>  }
>
> -#define MAX_TEST 13
> +#define MAX_TEST 14
>  #define MAX_PERF_TEST 3
>  int main(int argc, char **argv)
>  {
> @@ -500,6 +506,10 @@ int main(int argc, char **argv)
>  	test_cases[12] = MAKE_TEST(PUD, PUD, _2GB, NON_OVERLAPPING, EXPECT_SUCCESS,
>  				   "2GB mremap - Source PUD-aligned, Destination PUD-aligned");
>
> +	/* Src and Dest addr 1MB aligned. 5MB mremap. */
> +	test_cases[13] = MAKE_TEST(_1MB, _1MB, _5MB, NON_OVERLAPPING, EXPECT_SUCCESS,
> +				  "5MB mremap - Source 1MB-aligned, Destination 1MB-aligned");
> +
>  	perf_test_cases[0] =  MAKE_TEST(page_size, page_size, _1GB, NON_OVERLAPPING, EXPECT_SUCCESS,
>  					"1GB mremap - Source PTE-aligned, Destination PTE-aligned");
>  	/*
> --
> 2.42.0.rc1.204.g551eb34607-goog
>

Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>