[PATCH] hmm-tests: Fix migrate_dirty_page test

[PATCH] hmm-tests: Fix migrate_dirty_page test

[Alistair Popple]

As noted by John Hubbard the original test relied on side effects of the
implementation of migrate_vma_setup() to detect if pages had been
swapped to disk or not. This is subject to change in future so
explicitly check for swap entries via pagemap instead. Fix a spelling
mistake while we're at it.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
Fixes: 5cc88e844e87 ("selftests/hmm-tests: add test for dirty bits")
---
 tools/testing/selftests/vm/hmm-tests.c | 50 +++++++++++++++++++++++---
 1 file changed, 46 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/vm/hmm-tests.c b/tools/testing/selftests/vm/hmm-tests.c
index 70fdb49b59ed..b5f6a7dc1f12 100644
--- a/tools/testing/selftests/vm/hmm-tests.c
+++ b/tools/testing/selftests/vm/hmm-tests.c
@@ -1261,9 +1261,47 @@ static int destroy_cgroup(void)
 	return 0;
 }
 
+static uint64_t get_pfn(int fd, uint64_t ptr)
+{
+	uint64_t pfn;
+	int ret;
+
+	ret = pread(fd, &pfn, sizeof(ptr),
+		(uint64_t) ptr / getpagesize() * sizeof(ptr));
+	if (ret != sizeof(ptr))
+		return 0;
+
+	return pfn;
+}
+
+#define PAGEMAP_SWAPPED (1ULL << 62)
+
+/* Returns true if at least one page in the range is on swap */
+static bool pages_swapped(void *ptr, unsigned long pages)
+{
+	uint64_t pfn;
+	int fd = open("/proc/self/pagemap", O_RDONLY);
+	unsigned long i;
+
+	if (fd < 0)
+		return false;
+
+	for (i = 0; i < pages; i++) {
+		pfn = get_pfn(fd, (uint64_t) ptr + i * getpagesize());
+
+		if (pfn & PAGEMAP_SWAPPED) {
+			close(fd);
+			return true;
+		}
+	}
+
+	close(fd);
+	return false;
+}
+
 /*
  * Try and migrate a dirty page that has previously been swapped to disk. This
- * checks that we don't loose dirty bits.
+ * checks that we don't lose dirty bits.
  */
 TEST_F(hmm, migrate_dirty_page)
 {
@@ -1300,6 +1338,10 @@ TEST_F(hmm, migrate_dirty_page)
 
 	ASSERT_FALSE(write_cgroup_param(cgroup, "memory.reclaim", 1UL<<30));
 
+	/* Make sure at least some pages got paged to disk. */
+	if (!pages_swapped(buffer->ptr, npages))
+		SKIP(return, "Pages weren't swapped when they should have been");
+
 	/* Fault pages back in from swap as clean pages */
 	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
 		tmp += ptr[i];
@@ -1309,10 +1351,10 @@ TEST_F(hmm, migrate_dirty_page)
 		ptr[i] = i;
 
 	/*
-	 * Attempt to migrate memory to device, which should fail because
-	 * hopefully some pages are backed by swap storage.
+	 * Attempt to migrate memory to device. This might fail if some pages
+	 * are/were backed by swap but that's ok.
 	 */
-	ASSERT_TRUE(hmm_migrate_sys_to_dev(self->fd, buffer, npages));
+	hmm_migrate_sys_to_dev(self->fd, buffer, npages);
 
 	ASSERT_FALSE(write_cgroup_param(cgroup, "memory.reclaim", 1UL<<30));
 
-- 
2.35.1

Re: [PATCH] hmm-tests: Fix migrate_dirty_page test

[Mika Penttilä]

On 13.9.2022 8.22, Alistair Popple wrote:
> As noted by John Hubbard the original test relied on side effects of the
> implementation of migrate_vma_setup() to detect if pages had been
> swapped to disk or not. This is subject to change in future so
> explicitly check for swap entries via pagemap instead. Fix a spelling
> mistake while we're at it.
> 
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> Fixes: 5cc88e844e87 ("selftests/hmm-tests: add test for dirty bits")
> ---
>   tools/testing/selftests/vm/hmm-tests.c | 50 +++++++++++++++++++++++---
>   1 file changed, 46 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/vm/hmm-tests.c b/tools/testing/selftests/vm/hmm-tests.c
> index 70fdb49b59ed..b5f6a7dc1f12 100644
> --- a/tools/testing/selftests/vm/hmm-tests.c
> +++ b/tools/testing/selftests/vm/hmm-tests.c
> @@ -1261,9 +1261,47 @@ static int destroy_cgroup(void)
>   	return 0;
>   }
>   
> +static uint64_t get_pfn(int fd, uint64_t ptr)
> +{
> +	uint64_t pfn;
> +	int ret;
> +
> +	ret = pread(fd, &pfn, sizeof(ptr),
> +		(uint64_t) ptr / getpagesize() * sizeof(ptr));
> +	if (ret != sizeof(ptr))
> +		return 0;
> +
> +	return pfn;
> +}
> +
> +#define PAGEMAP_SWAPPED (1ULL << 62)
> +
> +/* Returns true if at least one page in the range is on swap */
> +static bool pages_swapped(void *ptr, unsigned long pages)
> +{
> +	uint64_t pfn;
> +	int fd = open("/proc/self/pagemap", O_RDONLY);
> +	unsigned long i;
> +
> +	if (fd < 0)
> +		return false;
> +
> +	for (i = 0; i < pages; i++) {
> +		pfn = get_pfn(fd, (uint64_t) ptr + i * getpagesize());
> +
> +		if (pfn & PAGEMAP_SWAPPED) {
> +			close(fd);
> +			return true;
> +		}
> +	}
> +
> +	close(fd);
> +	return false;
> +}
> +
>   /*
>    * Try and migrate a dirty page that has previously been swapped to disk. This
> - * checks that we don't loose dirty bits.
> + * checks that we don't lose dirty bits.
>    */
>   TEST_F(hmm, migrate_dirty_page)
>   {
> @@ -1300,6 +1338,10 @@ TEST_F(hmm, migrate_dirty_page)
>   
>   	ASSERT_FALSE(write_cgroup_param(cgroup, "memory.reclaim", 1UL<<30));
>   
> +	/* Make sure at least some pages got paged to disk. */
> +	if (!pages_swapped(buffer->ptr, npages))
> +		SKIP(return, "Pages weren't swapped when they should have been");
> +
>   	/* Fault pages back in from swap as clean pages */
>   	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
>   		tmp += ptr[i];
> @@ -1309,10 +1351,10 @@ TEST_F(hmm, migrate_dirty_page)
>   		ptr[i] = i;
>   
>   	/*
> -	 * Attempt to migrate memory to device, which should fail because
> -	 * hopefully some pages are backed by swap storage.
> +	 * Attempt to migrate memory to device. This might fail if some pages
> +	 * are/were backed by swap but that's ok.
>   	 */
> -	ASSERT_TRUE(hmm_migrate_sys_to_dev(self->fd, buffer, npages));
> +	hmm_migrate_sys_to_dev(self->fd, buffer, npages);
>   
>   	ASSERT_FALSE(write_cgroup_param(cgroup, "memory.reclaim", 1UL<<30));
>   


Reviewed-by: Mika Penttilä <mpenttil@redhat.com>

Re: [PATCH] hmm-tests: Fix migrate_dirty_page test

[David Hildenbrand]

On 13.09.22 07:22, Alistair Popple wrote:
> As noted by John Hubbard the original test relied on side effects of the
> implementation of migrate_vma_setup() to detect if pages had been
> swapped to disk or not. This is subject to change in future so
> explicitly check for swap entries via pagemap instead. Fix a spelling
> mistake while we're at it.
> 
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> Fixes: 5cc88e844e87 ("selftests/hmm-tests: add test for dirty bits")
> ---
>   tools/testing/selftests/vm/hmm-tests.c | 50 +++++++++++++++++++++++---
>   1 file changed, 46 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/vm/hmm-tests.c b/tools/testing/selftests/vm/hmm-tests.c
> index 70fdb49b59ed..b5f6a7dc1f12 100644
> --- a/tools/testing/selftests/vm/hmm-tests.c
> +++ b/tools/testing/selftests/vm/hmm-tests.c
> @@ -1261,9 +1261,47 @@ static int destroy_cgroup(void)
>   	return 0;
>   }
>   
> +static uint64_t get_pfn(int fd, uint64_t ptr)
> +{
> +	uint64_t pfn;
> +	int ret;
> +
> +	ret = pread(fd, &pfn, sizeof(ptr),
> +		(uint64_t) ptr / getpagesize() * sizeof(ptr));
> +	if (ret != sizeof(ptr))
> +		return 0;
> +
> +	return pfn;
> +}
> +
> +#define PAGEMAP_SWAPPED (1ULL << 62)
> +
> +/* Returns true if at least one page in the range is on swap */
> +static bool pages_swapped(void *ptr, unsigned long pages)
> +{
> +	uint64_t pfn;
> +	int fd = open("/proc/self/pagemap", O_RDONLY);
> +	unsigned long i;
> +
> +	if (fd < 0)
> +		return false;
> +
> +	for (i = 0; i < pages; i++) {
> +		pfn = get_pfn(fd, (uint64_t) ptr + i * getpagesize());
> +
> +		if (pfn & PAGEMAP_SWAPPED) {
> +			close(fd);
> +			return true;
> +		}

We do have pagemap_get_entry() in vm_util.c to query the pagemap entry.

Can you further, add pagemap_is_swapped() to vm_util.c?

I'll be also needing that (including a variant for testing a range) in 
anon COW tests.


-- 
Thanks,

David / dhildenb

Re: [PATCH] hmm-tests: Fix migrate_dirty_page test

[Alistair Popple]

David Hildenbrand <david@redhat.com> writes:

> On 13.09.22 07:22, Alistair Popple wrote:
>> As noted by John Hubbard the original test relied on side effects of the
>> implementation of migrate_vma_setup() to detect if pages had been
>> swapped to disk or not. This is subject to change in future so
>> explicitly check for swap entries via pagemap instead. Fix a spelling
>> mistake while we're at it.
>> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>> Fixes: 5cc88e844e87 ("selftests/hmm-tests: add test for dirty bits")
>> ---
>>   tools/testing/selftests/vm/hmm-tests.c | 50 +++++++++++++++++++++++---
>>   1 file changed, 46 insertions(+), 4 deletions(-)
>> diff --git a/tools/testing/selftests/vm/hmm-tests.c
>> b/tools/testing/selftests/vm/hmm-tests.c
>> index 70fdb49b59ed..b5f6a7dc1f12 100644
>> --- a/tools/testing/selftests/vm/hmm-tests.c
>> +++ b/tools/testing/selftests/vm/hmm-tests.c
>> @@ -1261,9 +1261,47 @@ static int destroy_cgroup(void)
>>   	return 0;
>>   }
>>   +static uint64_t get_pfn(int fd, uint64_t ptr)
>> +{
>> +	uint64_t pfn;
>> +	int ret;
>> +
>> +	ret = pread(fd, &pfn, sizeof(ptr),
>> +		(uint64_t) ptr / getpagesize() * sizeof(ptr));
>> +	if (ret != sizeof(ptr))
>> +		return 0;
>> +
>> +	return pfn;
>> +}
>> +
>> +#define PAGEMAP_SWAPPED (1ULL << 62)
>> +
>> +/* Returns true if at least one page in the range is on swap */
>> +static bool pages_swapped(void *ptr, unsigned long pages)
>> +{
>> +	uint64_t pfn;
>> +	int fd = open("/proc/self/pagemap", O_RDONLY);
>> +	unsigned long i;
>> +
>> +	if (fd < 0)
>> +		return false;
>> +
>> +	for (i = 0; i < pages; i++) {
>> +		pfn = get_pfn(fd, (uint64_t) ptr + i * getpagesize());
>> +
>> +		if (pfn & PAGEMAP_SWAPPED) {
>> +			close(fd);
>> +			return true;
>> +		}
>
> We do have pagemap_get_entry() in vm_util.c to query the pagemap entry.

Thanks. I'd missed that, although `grep pagemap
tools/testing/selftests/vm` suggests I'm not the first to follow a
tradition of open-coding this :-)

But there's no need to perpetuate that tradition, so will redo this to
use vm_util.c instead.

> Can you further, add pagemap_is_swapped() to vm_util.c?
>
> I'll be also needing that (including a variant for testing a range) in anon COW
> tests.

Re: [PATCH] hmm-tests: Fix migrate_dirty_page test

[David Hildenbrand]

On 13.09.22 10:20, Alistair Popple wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 13.09.22 07:22, Alistair Popple wrote:
>>> As noted by John Hubbard the original test relied on side effects of the
>>> implementation of migrate_vma_setup() to detect if pages had been
>>> swapped to disk or not. This is subject to change in future so
>>> explicitly check for swap entries via pagemap instead. Fix a spelling
>>> mistake while we're at it.
>>> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>>> Fixes: 5cc88e844e87 ("selftests/hmm-tests: add test for dirty bits")
>>> ---
>>>    tools/testing/selftests/vm/hmm-tests.c | 50 +++++++++++++++++++++++---
>>>    1 file changed, 46 insertions(+), 4 deletions(-)
>>> diff --git a/tools/testing/selftests/vm/hmm-tests.c
>>> b/tools/testing/selftests/vm/hmm-tests.c
>>> index 70fdb49b59ed..b5f6a7dc1f12 100644
>>> --- a/tools/testing/selftests/vm/hmm-tests.c
>>> +++ b/tools/testing/selftests/vm/hmm-tests.c
>>> @@ -1261,9 +1261,47 @@ static int destroy_cgroup(void)
>>>    	return 0;
>>>    }
>>>    +static uint64_t get_pfn(int fd, uint64_t ptr)
>>> +{
>>> +	uint64_t pfn;
>>> +	int ret;
>>> +
>>> +	ret = pread(fd, &pfn, sizeof(ptr),
>>> +		(uint64_t) ptr / getpagesize() * sizeof(ptr));
>>> +	if (ret != sizeof(ptr))
>>> +		return 0;
>>> +
>>> +	return pfn;
>>> +}
>>> +
>>> +#define PAGEMAP_SWAPPED (1ULL << 62)
>>> +
>>> +/* Returns true if at least one page in the range is on swap */
>>> +static bool pages_swapped(void *ptr, unsigned long pages)
>>> +{
>>> +	uint64_t pfn;
>>> +	int fd = open("/proc/self/pagemap", O_RDONLY);
>>> +	unsigned long i;
>>> +
>>> +	if (fd < 0)
>>> +		return false;
>>> +
>>> +	for (i = 0; i < pages; i++) {
>>> +		pfn = get_pfn(fd, (uint64_t) ptr + i * getpagesize());
>>> +
>>> +		if (pfn & PAGEMAP_SWAPPED) {
>>> +			close(fd);
>>> +			return true;
>>> +		}
>>
>> We do have pagemap_get_entry() in vm_util.c to query the pagemap entry.
> 
> Thanks. I'd missed that, although `grep pagemap
> tools/testing/selftests/vm` suggests I'm not the first to follow a
> tradition of open-coding this :-)
> 
> But there's no need to perpetuate that tradition, so will redo this to
> use vm_util.c instead.

Yeah, we just recently factored stuff out into there. I'll be factoring 
out more in my upcoming tests from the madv_populate tests.

-- 
Thanks,

David / dhildenb