Re: [PATCH v2 1/2] selftest/vm: Use correct PAGE_SHIFT value for ppc64

[Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>]

On 2/11/22 16:03, Mike Rapoport wrote:
> On Fri, Feb 11, 2022 at 12:03:28PM +0530, Aneesh Kumar K.V wrote:
>> Keep it simple by using a #define and limiting hugepage size to 2M.
>> This keeps the test simpler instead of dynamically finding the page size
>> and huge page size.
>>
>> Without this tests are broken w.r.t reading /proc/self/pagemap
>>
>> 	if (pread(pagemap_fd, ent, sizeof(ent),
>> 			(uintptr_t)ptr >> (PAGE_SHIFT - 3)) != sizeof(ent))
>> 		err(2, "read pagemap");
>>
>> Cc: Shuah Khan <shuah@kernel.org>
>> Cc: linux-kselftest@vger.kernel.org
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>>   tools/testing/selftests/vm/ksm_tests.c        | 9 ++++++++-
>>   tools/testing/selftests/vm/transhuge-stress.c | 9 ++++++++-
>>   2 files changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/vm/ksm_tests.c b/tools/testing/selftests/vm/ksm_tests.c
>> index 1436e1a9a3d3..cae72872152b 100644
>> --- a/tools/testing/selftests/vm/ksm_tests.c
>> +++ b/tools/testing/selftests/vm/ksm_tests.c
>> @@ -22,7 +22,14 @@
>>   #define KSM_MERGE_ACROSS_NODES_DEFAULT true
>>   #define MB (1ul << 20)
>>   
>> -#define PAGE_SHIFT 12
>> +#ifdef __powerpc64__
>> +#define PAGE_SHIFT	16
>> +#else
>> +#define PAGE_SHIFT	12
>> +#endif
> 
> Page size can be other than 4096 for other configurations as well. And even
> on ppc64 it's not necessarily 64k.
> 

But most common test config is with 64K page size.

> Ideally page size in selftests/vm should be sysconf(_SC_PAGESIZE)


yes. As explained in commit message, the idea was to keep it simpler.

"Keep it simple by using a #define and limiting hugepage size to 2M.
This keeps the test simpler instead of dynamically finding the page size
and huge page size.

Without this tests are broken w.r.t reading /proc/self/pagemap"

We can definitely look at updating multiple tests in selftest/vm to work 
with dynamic value of pagesize and huagepage size. But that can be 
outside this patch?

> 
>> +/*
>> + * On ppc64 this will only work with radix 2M hugepage size
>> + */
>>   #define HPAGE_SHIFT 21
>>   
>>   #define PAGE_SIZE (1 << PAGE_SHIFT)
>> diff --git a/tools/testing/selftests/vm/transhuge-stress.c b/tools/testing/selftests/vm/transhuge-stress.c
>> index 5e4c036f6ad3..b1f8d98355c5 100644
>> --- a/tools/testing/selftests/vm/transhuge-stress.c
>> +++ b/tools/testing/selftests/vm/transhuge-stress.c
>> @@ -16,7 +16,14 @@
>>   #include <string.h>
>>   #include <sys/mman.h>
>>   
>> -#define PAGE_SHIFT 12
>> +#ifdef __powerpc64__
>> +#define PAGE_SHIFT	16
>> +#else
>> +#define PAGE_SHIFT	12
>> +#endif
>> +/*
>> + * On ppc64 this will only work with radix 2M hugepage size
>> + */
>>   #define HPAGE_SHIFT 21
>>   
>>   #define PAGE_SIZE (1 << PAGE_SHIFT)
>> -- 
>> 2.34.1
>>
>>
>