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

[wangyanan (Y)]

Hi Drew,

Thanks for your attention to this series!
On 2021/3/12 19:31, Andrew Jones wrote:
> 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@xxxxxxxxxx>
> > Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
> > ---
> >   .../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.
I think it's a good idea to output the errno together with it's string 
in TEST_ASSERT,
it will explicitly indicate that the string is an error information and 
the errno is much
easier to be used for debugging than the string. I will make this change 
a separate
patch in next version and add your S-b tag.
> > +
> > +	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?
This makes senses. But it should be %ld corresponding to size_t.

Thanks,
Yanan.
> > +	return size;
> > +}
> > +
> >   void backing_src_help(void)
> >   {
> >   	int i;
> > --
> > 2.23.0
> Thanks,
> drew
>
> .