linux-kernel - Re: [V2 PATCH 5/6] KVM: selftests: Add get_free_huge_2m

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Message-ID: <Y8cdWKaZVXQFcO+i@google.com>
Date:   Tue, 17 Jan 2023 22:12:40 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vishal Annapurve <vannapurve@...gle.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, pbonzini@...hat.com,
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Subject: Re: [V2 PATCH 5/6] KVM: selftests: Add get_free_huge_2m_pages

On Mon, Dec 05, 2022, Vishal Annapurve wrote:
> Add an API to query free 2MB hugepages in the system.
> 
> Signed-off-by: Vishal Annapurve <vannapurve@...gle.com>
> ---
>  .../testing/selftests/kvm/include/test_util.h  |  1 +
>  tools/testing/selftests/kvm/lib/test_util.c    | 18 ++++++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
> index aea80071f2b8..3d1cc215940a 100644
> --- a/tools/testing/selftests/kvm/include/test_util.h
> +++ b/tools/testing/selftests/kvm/include/test_util.h
> @@ -122,6 +122,7 @@ struct vm_mem_backing_src_alias {
>  bool thp_configured(void);
>  size_t get_trans_hugepagesz(void);
>  size_t get_def_hugetlb_pagesz(void);
> +size_t get_free_huge_2mb_pages(void);
>  const struct vm_mem_backing_src_alias *vm_mem_backing_src_alias(uint32_t i);
>  size_t get_backing_src_pagesz(uint32_t i);
>  bool is_backing_src_hugetlb(uint32_t i);
> diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
> index d33b98bfe8a3..745573023b57 100644
> --- a/tools/testing/selftests/kvm/lib/test_util.c
> +++ b/tools/testing/selftests/kvm/lib/test_util.c
> @@ -162,6 +162,24 @@ size_t get_trans_hugepagesz(void)
>  	return size;
>  }
>  
> +size_t get_free_huge_2mb_pages(void)

I strongly prefer to follow the precedence set by other tests, which at this
point means defaulting to non-huge pages.  I do think we need to make it easier
and/or automatic to test hugepages, but I would like to tackle that problem
separately.  E.g. a kernel built without hugepage support will fail the fopen()
below.

> +{
> +	size_t free_pages;
> +	FILE *f;
> +	int ret;
> +
> +	f = fopen("/sys/kernel/mm/hugepages/hugepages-2048kB/free_hugepages", "r");
> +	TEST_ASSERT(f != NULL, "Error in opening hugepages-2048kB/free_hugepages");
> +
> +	do {
> +		ret = fscanf(f, "%ld", &free_pages);
> +	} while (errno == EINTR);
> +	TEST_ASSERT(ret < 1, "Error reading hugepages-2048kB/free_hugepages");
> +	fclose(f);
> +
> +	return free_pages;
> +}
> +
>  size_t get_def_hugetlb_pagesz(void)
>  {
>  	char buf[64];
> -- 
> 2.39.0.rc0.267.gcb52ba06e7-goog
>