Re: ksm: add mremap selftests for ksm_rmap_walk

["Lorenzo Stoakes (Oracle)" <ljs@kernel.org>]

On Tue, Apr 07, 2026 at 02:08:05PM +0800, xu.xin16@zte.com.cn wrote:
> From: xu xin <xu.xin16@zte.com.cn>
>
> The existing tools/testing/selftests/mm/rmap.c has already one testcase
> for ksm_rmap_walk in TEST_F(migrate, ksm), which takes use of migration
> of page from one NUMA node to another NUMA node. However, it just lacks
> the senario of mremapped VMAs.
>
> Before migrating, we add the calling of mremap() to address mapped with KSM
> pages, which is specailly to test a optimization which is introduced by this
> patch ("ksm: Optimize rmap_walk_ksm by passing a suitable address range")
> https://lore.kernel.org/all/20260212193045556CbzCX8p9gDu73tQ2nvHEI@zte.com.cn/
>
> Result:
> TAP version 13
> 1..5
> ok 1 migrate.anon
> ok 2 migrate.shm
> ok 3 migrate.file # SKIP Failed in worker
> ok 4 migrate.ksm
> ok 5 migrate.ksm_and_mremap
>
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>

Thanks for this, tests are always good, but I think we should bundle this in the
same series as with the rmap_walk_ksm optimisation, assuming we can be sure
whatever-form-of-that-we-end-up-with is ok.

I currently share Hugh's doubts as to correctness, so let's put the two together
I think.

Cheers, Lorenzo

> ---
>  tools/testing/selftests/mm/rmap.c    | 69 ++++++++++++++++++++++++++++
>  tools/testing/selftests/mm/vm_util.c | 38 +++++++++++++++
>  tools/testing/selftests/mm/vm_util.h |  2 +
>  3 files changed, 109 insertions(+)
>
> diff --git a/tools/testing/selftests/mm/rmap.c b/tools/testing/selftests/mm/rmap.c
> index 53f2058b0ef2..65470def2bf1 100644
> --- a/tools/testing/selftests/mm/rmap.c
> +++ b/tools/testing/selftests/mm/rmap.c
> @@ -430,4 +430,73 @@ TEST_F(migrate, ksm)
>  	propagate_children(_metadata, data);
>  }
>
> +/* To test if ksm page can be migrated when it's mremapped */
> +int merge_mremap_and_migrate(struct global_data *data)
> +{
> +	int ret = 0;
> +	/* Allocate range and set the same data */
> +	data->mapsize = 3*getpagesize();
> +	data->region = mmap(NULL, data->mapsize, PROT_READ|PROT_WRITE,
> +			   MAP_PRIVATE|MAP_ANON, -1, 0);
> +	if (data->region == MAP_FAILED)
> +		ksft_exit_fail_perror("mmap failed");
> +
> +	memset(data->region, 0x77, data->mapsize);
> +
> +	if (ksm_start() < 0)
> +		return FAIL_ON_CHECK;
> +
> +	/* 1  2 expected */
> +	ksft_print_msg("Shared: %ld (1 expected) Sharing: %ld (2 expected)\n",
> +		ksm_get_pages_shared(), ksm_get_pages_sharing());
> +
> +	/*
> +	 * Mremap the second pagesize address range into the third pagesize
> +	 * address.
> +	 */
> +	data->region = mremap(data->region + getpagesize(), getpagesize(), getpagesize(),
> +			 MREMAP_MAYMOVE|MREMAP_FIXED, data->region + 2*getpagesize());
> +
> +	if (data->region == MAP_FAILED)
> +		return FAIL_ON_CHECK;
> +
> +	/* Check if we can migrate this region successfully */
> +	ret = try_to_move_page(data->region);
> +	if (ret != 0)
> +		return ret;
> +
> +	/* Wait ksm scan two turns at least */
> +	if (ksm_start() < 0)
> +		return FAIL_ON_CHECK;
> +
> +	/* 1  1 expected */
> +	ksft_print_msg("Shared: %ld (1 expected) Sharing: %ld (1 expected)\n",
> +		ksm_get_pages_shared(), ksm_get_pages_sharing());
> +
> +	return 0;
> +}
> +
> +TEST_F(migrate, ksm_and_mremap)
> +{
> +	int ret;
> +	struct global_data *data = &self->data;
> +
> +	/* prepare KSM interface setting */
> +	if (ksm_stop() < 0)
> +		SKIP(return, "accessing \"/sys/kernel/mm/ksm/run\") failed");
> +	if (ksm_get_full_scans() < 0)
> +		SKIP(return, "accessing \"/sys/kernel/mm/ksm/full_scan\") failed");
> +
> +	ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
> +	if (ret < 0 && errno == EINVAL)
> +		SKIP(return, "PR_SET_MEMORY_MERGE not supported");
> +	else if (ret)
> +		ksft_exit_fail_perror("PR_SET_MEMORY_MERGE=1 failed");
> +
> +	/* Start to merge same pages and mremap one of the three page area,
> +	 * and test if ksm page can be migrated when it's mremapped */
> +	ASSERT_EQ(merge_mremap_and_migrate(data), 0);
> +}
> +
> +
>  TEST_HARNESS_MAIN
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 9428f4d7bf55..47402b771ef8 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -646,6 +646,44 @@ long ksm_get_self_merging_pages(void)
>  	return strtol(buf, NULL, 10);
>  }
>
> +long ksm_get_pages_shared(void)
> +{
> +	int ksm_pages_shared_fd;
> +	char buf[10];
> +	ssize_t ret;
> +
> +	ksm_pages_shared_fd = open("/sys/kernel/mm/ksm/pages_shared", O_RDONLY);
> +	if (ksm_pages_shared_fd < 0)
> +		return -errno;
> +
> +	ret = pread(ksm_pages_shared_fd, buf, sizeof(buf) - 1, 0);
> +	close(ksm_pages_shared_fd);
> +	if (ret <= 0)
> +		return -errno;
> +	buf[ret] = 0;
> +
> +	return strtol(buf, NULL, 10);
> +}
> +
> +long ksm_get_pages_sharing(void)
> +{
> +	int ksm_pages_sharing_fd;
> +	char buf[10];
> +	ssize_t ret;
> +
> +	ksm_pages_sharing_fd = open("/sys/kernel/mm/ksm/pages_sharing", O_RDONLY);
> +	if (ksm_pages_sharing_fd < 0)
> +		return -errno;
> +
> +	ret = pread(ksm_pages_sharing_fd, buf, sizeof(buf) - 1, 0);
> +	close(ksm_pages_sharing_fd);
> +	if (ret <= 0)
> +		return -errno;
> +	buf[ret] = 0;
> +
> +	return strtol(buf, NULL, 10);
> +}
> +
>  long ksm_get_full_scans(void)
>  {
>  	int ksm_full_scans_fd;
> diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
> index e9c4e24769c1..b0dd190f83e4 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -151,6 +151,8 @@ void *sys_mremap(void *old_address, unsigned long old_size,
>
>  long ksm_get_self_zero_pages(void);
>  long ksm_get_self_merging_pages(void);
> +long ksm_get_pages_shared(void);
> +long ksm_get_pages_sharing(void);
>  long ksm_get_full_scans(void);
>  int ksm_use_zero_pages(void);
>  int ksm_start(void);
> --
> 2.25.1