linux-kernel - Re: [PATCH] SelfTest: KVM: Drop Asserts for madvise failures

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Message-ID: <20181116091138.zcqczgxdlzanceee@kamzik.brq.redhat.com>
Date:   Fri, 16 Nov 2018 10:11:38 +0100
From:   Andrew Jones <drjones@...hat.com>
To:     Ahmed Abd El Mawgood <ahmedsoliman@...a.vt.edu>
Cc:     Shuah Khan <shuah@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Colin Ian King <colin.king@...onical.com>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hossam Hassan <7ossam9063@...il.com>,
        Ahmed Lotfy <A7med.lotfey@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Anders Roxell <anders.roxell@...aro.org>
Subject: Re: [PATCH] SelfTest: KVM: Drop Asserts for madvise failures

On Thu, Nov 15, 2018 at 08:09:07PM +0200, Ahmed Abd El Mawgood wrote:
> From: Ahmed Abd El Mawgood <ahmedsoliman@...a.vt.edu>
> 
> madvise() returns -1 without CONFIG_TRANSPARENT_HUGEPAGE=y. That would
> trigger asserts when checking for return value of madvice. Following
> similar decision to [1]. I thought it is ok to assume that madvise()
> failures implies that THP is not supported by host kernel.
> 
> Other options were to check for Transparent Huge Page support in
> /sys/kernel/mm/transparent_hugepage/enabled.
> 
> -- links --
> [1] https://lists.gnu.org/archive/html/qemu-devel/2015-11/msg04514.html
> 
> Signed-off-by: Ahmed Abd El Mawgood <ahmedsoliman@...a.vt.edu>
> ---
>  tools/testing/selftests/kvm/lib/kvm_util.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 1b41e71283d5..7725cfdf1b79 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -586,14 +586,12 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
>  				 src_type == VM_MEM_SRC_ANONYMOUS_THP ?  huge_page_size : 1);
>  
>  	/* As needed perform madvise */
> -	if (src_type == VM_MEM_SRC_ANONYMOUS || src_type == VM_MEM_SRC_ANONYMOUS_THP) {
> -		ret = madvise(region->host_mem, npages * vm->page_size,
> -			     src_type == VM_MEM_SRC_ANONYMOUS ? MADV_NOHUGEPAGE : MADV_HUGEPAGE);
> -		TEST_ASSERT(ret == 0, "madvise failed,\n"
> -			    "  addr: %p\n"
> -			    "  length: 0x%lx\n"
> -			    "  src_type: %x",
> -			    region->host_mem, npages * vm->page_size, src_type);
> +	if (src_type == VM_MEM_SRC_ANONYMOUS) {
> +		madvise(region->host_mem, npages * vm->page_size,
> +				MADV_NOHUGEPAGE);

This is fine.

> +	} else if (src_type == VM_MEM_SRC_ANONYMOUS_THP) {
> +		madvise(region->host_mem, npages * vm->page_size,
> +				MADV_HUGEPAGE);

I would still assert here, but with a more informative message like
"madvise(MADV_HUGEPAGE) failed. Does the kernel have
CONFIG_TRANSPARENT_HUGEPAGE=y?"

>  	}
>  
>  	region->unused_phy_pages = sparsebit_alloc();
> -- 
> 2.18.1
> 

Thanks,
drew