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

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Date:   Mon, 22 Mar 2021 14:42:41 +0800
From:   "wangyanan (Y)" <wangyanan55@...wei.com>
To:     Andrew Jones <drjones@...hat.com>
CC:     <kvm@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Ben Gardon" <bgardon@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "Vitaly Kuznetsov" <vkuznets@...hat.com>,
        Peter Xu <peterx@...hat.com>, Marc Zyngier <maz@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...hat.com>,
        "Arnaldo Carvalho de Melo" <acme@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        <wanghaibin.wang@...wei.com>, <yezengruan@...wei.com>,
        <yuzenghui@...wei.com>
Subject: Re: [RFC PATCH v4 5/9] KVM: selftests: Add a helper to get system
 configured THP page size

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@...wei.com>
>> Reviewed-by: Ben Gardon <bgardon@...gle.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.
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
>
> .