Re: [RFC PATCH v4 5/9] KVM: selftests: Add a helper to get system configured THP page size

[Andrew Jones <drjones@redhat.com>]

On Tue, Mar 02, 2021 at 08:57:47PM +0800, Yanan Wang wrote:
> If we want to have some tests about transparent hugepages, the system
> configured THP hugepage size should better be known by the tests, which
> can be used for kinds of alignment or guest memory accessing of vcpus...
> So it makes sense to add a helper to get the transparent hugepage size.
> 
> With VM_MEM_SRC_ANONYMOUS_THP specified in vm_userspace_mem_region_add(),
> we now stat /sys/kernel/mm/transparent_hugepage to check whether THP is
> configured in the host kernel before madvise(). Based on this, we can also
> read file /sys/kernel/mm/transparent_hugepage/hpage_pmd_size to get THP
> hugepage size.
> 
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> Reviewed-by: Ben Gardon <bgardon@google.com>
> ---
>  .../testing/selftests/kvm/include/test_util.h |  2 ++
>  tools/testing/selftests/kvm/lib/test_util.c   | 36 +++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
> index b7f41399f22c..ef24c76ba89a 100644
> --- a/tools/testing/selftests/kvm/include/test_util.h
> +++ b/tools/testing/selftests/kvm/include/test_util.h
> @@ -78,6 +78,8 @@ struct vm_mem_backing_src_alias {
>  	enum vm_mem_backing_src_type type;
>  };
>  
> +bool thp_configured(void);
> +size_t get_trans_hugepagesz(void);
>  void backing_src_help(void);
>  enum vm_mem_backing_src_type parse_backing_src_type(const char *type_name);
>  
> diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
> index c7c0627c6842..f2d133f76c67 100644
> --- a/tools/testing/selftests/kvm/lib/test_util.c
> +++ b/tools/testing/selftests/kvm/lib/test_util.c
> @@ -10,6 +10,7 @@
>  #include <limits.h>
>  #include <stdlib.h>
>  #include <time.h>
> +#include <sys/stat.h>
>  #include "linux/kernel.h"
>  
>  #include "test_util.h"
> @@ -117,6 +118,41 @@ const struct vm_mem_backing_src_alias backing_src_aliases[] = {
>  	{"anonymous_hugetlb", VM_MEM_SRC_ANONYMOUS_HUGETLB,},
>  };
>  
> +bool thp_configured(void)
> +{
> +	int ret;
> +	struct stat statbuf;
> +
> +	ret = stat("/sys/kernel/mm/transparent_hugepage", &statbuf);
> +	TEST_ASSERT(ret == 0 || (ret == -1 && errno == ENOENT),
> +		    "Error in stating /sys/kernel/mm/transparent_hugepage: %d",
> +		    errno);

TEST_ASSERT will already output errno's string. Is that not sufficient? If
not, I think extending TEST_ASSERT to output errno too would be fine.

> +
> +	return ret == 0;
> +}
> +
> +size_t get_trans_hugepagesz(void)
> +{
> +	size_t size;
> +	char buf[16];
> +	FILE *f;
> +
> +	TEST_ASSERT(thp_configured(), "THP is not configured in host kernel");
> +
> +	f = fopen("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size", "r");
> +	TEST_ASSERT(f != NULL,
> +		    "Error in opening transparent_hugepage/hpage_pmd_size: %d",
> +		    errno);

Same comment as above.

> +
> +	if (fread(buf, sizeof(char), sizeof(buf), f) == 0) {
> +		fclose(f);
> +		TEST_FAIL("Unable to read transparent_hugepage/hpage_pmd_size");
> +	}
> +
> +	size = strtoull(buf, NULL, 10);

fscanf with %lld?

> +	return size;
> +}
> +
>  void backing_src_help(void)
>  {
>  	int i;
> -- 
> 2.23.0
> 

Thanks,
drew