diff mbox series

[v3,6/7] selftest/mm: ksm_functional_tests: test in mmap_and_merge_range() if anything got merged

Message ID 20230803143208.383663-7-david@redhat.com (mailing list archive)
State New
Headers show
Series smaps / mm/gup: fix gup_can_follow_protnone fallout | expand

Commit Message

David Hildenbrand Aug. 3, 2023, 2:32 p.m. UTC
Let's extend mmap_and_merge_range() to test if anything in the current
process was merged. range_maps_duplicates() is too unreliable for that
use case, so instead look at KSM stats.

Trigger a complete unmerge first, to cleanup the stable tree and
stabilize accounting of merged pages.

Note that we're using /proc/self/ksm_merging_pages instead of
/proc/self/ksm_stat, because that one is available in more existing
kernels.

If /proc/self/ksm_merging_pages can't be opened, we can't perform any
checks and simply skip them.

We have to special-case the shared zeropage for now. But the only user
-- test_unmerge_zero_pages() -- performs its own merge checks.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 .../selftests/mm/ksm_functional_tests.c       | 47 +++++++++++++++++++
 1 file changed, 47 insertions(+)

Comments

Peter Xu Aug. 3, 2023, 7:05 p.m. UTC | #1
On Thu, Aug 03, 2023 at 04:32:07PM +0200, David Hildenbrand wrote:
> Let's extend mmap_and_merge_range() to test if anything in the current
> process was merged. range_maps_duplicates() is too unreliable for that
> use case, so instead look at KSM stats.
> 
> Trigger a complete unmerge first, to cleanup the stable tree and
> stabilize accounting of merged pages.
> 
> Note that we're using /proc/self/ksm_merging_pages instead of
> /proc/self/ksm_stat, because that one is available in more existing
> kernels.
> 
> If /proc/self/ksm_merging_pages can't be opened, we can't perform any
> checks and simply skip them.
> 
> We have to special-case the shared zeropage for now. But the only user
> -- test_unmerge_zero_pages() -- performs its own merge checks.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Peter Xu <peterx@redhat.com>

One nitpick:

> ---
>  .../selftests/mm/ksm_functional_tests.c       | 47 +++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> index 0de9d33cd565..cb63b600cb4f 100644
> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> @@ -30,6 +30,7 @@
>  static int ksm_fd;
>  static int ksm_full_scans_fd;
>  static int proc_self_ksm_stat_fd;
> +static int proc_self_ksm_merging_pages_fd;
>  static int ksm_use_zero_pages_fd;
>  static int pagemap_fd;
>  static size_t pagesize;
> @@ -88,6 +89,22 @@ static long get_my_ksm_zero_pages(void)
>  	return my_ksm_zero_pages;
>  }
>  
> +static long get_my_merging_pages(void)
> +{
> +	char buf[10];
> +	ssize_t ret;
> +
> +	if (proc_self_ksm_merging_pages_fd < 0)
> +		return proc_self_ksm_merging_pages_fd;

Better do the fds check all in main(), e.g. not all callers below considers
negative values, so -1 can pass "if (get_my_merging_pages())" etc.

> +
> +	ret = pread(proc_self_ksm_merging_pages_fd, buf, sizeof(buf) - 1, 0);
> +	if (ret <= 0)
> +		return -errno;
> +	buf[ret] = 0;
> +
> +	return strtol(buf, NULL, 10);
> +}
David Hildenbrand Aug. 4, 2023, 5:56 p.m. UTC | #2
On 03.08.23 21:05, Peter Xu wrote:
> On Thu, Aug 03, 2023 at 04:32:07PM +0200, David Hildenbrand wrote:
>> Let's extend mmap_and_merge_range() to test if anything in the current
>> process was merged. range_maps_duplicates() is too unreliable for that
>> use case, so instead look at KSM stats.
>>
>> Trigger a complete unmerge first, to cleanup the stable tree and
>> stabilize accounting of merged pages.
>>
>> Note that we're using /proc/self/ksm_merging_pages instead of
>> /proc/self/ksm_stat, because that one is available in more existing
>> kernels.
>>
>> If /proc/self/ksm_merging_pages can't be opened, we can't perform any
>> checks and simply skip them.
>>
>> We have to special-case the shared zeropage for now. But the only user
>> -- test_unmerge_zero_pages() -- performs its own merge checks.
>>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 

Hi Peter,

thanks for the review!

> Acked-by: Peter Xu <peterx@redhat.com>
> 
> One nitpick:
> 
>> ---
>>   .../selftests/mm/ksm_functional_tests.c       | 47 +++++++++++++++++++
>>   1 file changed, 47 insertions(+)
>>
>> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
>> index 0de9d33cd565..cb63b600cb4f 100644
>> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
>> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
>> @@ -30,6 +30,7 @@
>>   static int ksm_fd;
>>   static int ksm_full_scans_fd;
>>   static int proc_self_ksm_stat_fd;
>> +static int proc_self_ksm_merging_pages_fd;
>>   static int ksm_use_zero_pages_fd;
>>   static int pagemap_fd;
>>   static size_t pagesize;
>> @@ -88,6 +89,22 @@ static long get_my_ksm_zero_pages(void)
>>   	return my_ksm_zero_pages;
>>   }
>>   
>> +static long get_my_merging_pages(void)
>> +{
>> +	char buf[10];
>> +	ssize_t ret;
>> +
>> +	if (proc_self_ksm_merging_pages_fd < 0)
>> +		return proc_self_ksm_merging_pages_fd;
> 
> Better do the fds check all in main(), e.g. not all callers below considers
> negative values, so -1 can pass "if (get_my_merging_pages())" etc.

The two existing callers should be handling it correctly:

if (get_my_merging_pages() > 0)
	-> fail

if (val && !get_my_merging_pages()
	-> fail

Both will pass on negative values, unless I am missing something.

I tried to keep the test working also on older kernels where 
ksm_merging_pages does not exist yet (it's ~1 year old).


Anyhow, if you think it's better to make the test fail on these setups, 
I can change it.
diff mbox series

Patch

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 0de9d33cd565..cb63b600cb4f 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -30,6 +30,7 @@ 
 static int ksm_fd;
 static int ksm_full_scans_fd;
 static int proc_self_ksm_stat_fd;
+static int proc_self_ksm_merging_pages_fd;
 static int ksm_use_zero_pages_fd;
 static int pagemap_fd;
 static size_t pagesize;
@@ -88,6 +89,22 @@  static long get_my_ksm_zero_pages(void)
 	return my_ksm_zero_pages;
 }
 
+static long get_my_merging_pages(void)
+{
+	char buf[10];
+	ssize_t ret;
+
+	if (proc_self_ksm_merging_pages_fd < 0)
+		return proc_self_ksm_merging_pages_fd;
+
+	ret = pread(proc_self_ksm_merging_pages_fd, buf, sizeof(buf) - 1, 0);
+	if (ret <= 0)
+		return -errno;
+	buf[ret] = 0;
+
+	return strtol(buf, NULL, 10);
+}
+
 static long ksm_get_full_scans(void)
 {
 	char buf[10];
@@ -120,11 +137,29 @@  static int ksm_merge(void)
 	return 0;
 }
 
+static int ksm_unmerge(void)
+{
+	if (write(ksm_fd, "2", 1) != 1)
+		return -errno;
+	return 0;
+}
+
 static char *mmap_and_merge_range(char val, unsigned long size, bool use_prctl)
 {
 	char *map;
 	int ret;
 
+	/* Stabilize accounting by disabling KSM completely. */
+	if (ksm_unmerge()) {
+		ksft_test_result_fail("Disabling (unmerging) KSM failed\n");
+		goto unmap;
+	}
+
+	if (get_my_merging_pages() > 0) {
+		ksft_test_result_fail("Still pages merged\n");
+		goto unmap;
+	}
+
 	map = mmap(NULL, size, PROT_READ|PROT_WRITE,
 		   MAP_PRIVATE|MAP_ANON, -1, 0);
 	if (map == MAP_FAILED) {
@@ -160,6 +195,16 @@  static char *mmap_and_merge_range(char val, unsigned long size, bool use_prctl)
 		ksft_test_result_fail("Running KSM failed\n");
 		goto unmap;
 	}
+
+	/*
+	 * Check if anything was merged at all. Ignore the zero page that is
+	 * accounted differently (depending on kernel support).
+	 */
+	if (val && !get_my_merging_pages()) {
+		ksft_test_result_fail("No pages got merged\n");
+		goto unmap;
+	}
+
 	return map;
 unmap:
 	munmap(map, size);
@@ -473,6 +518,8 @@  int main(int argc, char **argv)
 	if (pagemap_fd < 0)
 		ksft_exit_skip("open(\"/proc/self/pagemap\") failed\n");
 	proc_self_ksm_stat_fd = open("/proc/self/ksm_stat", O_RDONLY);
+	proc_self_ksm_merging_pages_fd = open("/proc/self/ksm_merging_pages",
+					      O_RDONLY);
 	ksm_use_zero_pages_fd = open("/sys/kernel/mm/ksm/use_zero_pages", O_RDWR);
 
 	test_unmerge();