[PATCH blktests v0] nvme/029: reserve hugepages for lager allocations

[Shinichiro Kawasaki]

Thanks for the fix.

On Feb 20, 2024 / 09:13, Daniel Wagner wrote:
> The test is issuing larger IO workload. This depends on being able to
> allocate larger chucks of linear memory. nvme-cli used to use libhugetbl

I guess,

s/chuck/chunk/
s/libhugetbl/libhugetlb/

> to automatically allocate the HugeTBL pool. Though nvme-cli dropped the

s/HugeTBL/HugeTLB/

> dependency on the library, thus the test needs to provision the system
> accordingly.
> 
> Reported-by: Yi Zhang <yi.zhang at redhat.com>
> Tested-by: Yi Zhang <yi.zhang at redhat.com>
> Signed-off-by: Daniel Wagner <dwagner at suse.de>

I found the problem was reported and discussed in a GitHub issue [1]. How about
to add a "Link:" tag for reference?

[1] https://github.com/linux-nvme/nvme-cli/issues/2218

> ---
>  tests/nvme/029 | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/tests/nvme/029 b/tests/nvme/029
> index db6e8b91f707..7833fd29e235 100755
> --- a/tests/nvme/029
> +++ b/tests/nvme/029
> @@ -54,6 +54,7 @@ test() {
>  	_setup_nvmet
>  
>  	local nvmedev
> +	local reset_nr_hugepages=false
>  
>  	_nvmet_target_setup
>  
> @@ -62,6 +63,11 @@ test() {
>  	nvmedev=$(_find_nvme_dev "${def_subsysnqn}")
>  	_check_uuid "${nvmedev}"
>  
> +	if [[ "$(cat /proc/sys/vm/nr_hugepages)" -eq 0 ]]; then
> +		echo 20 > /proc/sys/vm/nr_hugepages
> +		reset_nr_hugepages=true
> +	fi

I found this changes makes the test case fail when the kernel does not have
CONFIG_HUGETLBFS. Without the config, /proc/sys/vm/nr_hugepages does not
exist.

When CONFIG_HUGETLBFS is not defined, should we skip this test case? If this is
the case, we can add "_have_kernel_option HUGETLBFS" in requires(). If not, we
should check existence of /proc/sys/vm/nr_hugepages before touching it, like:

       if [[ -r /proc/sys/vm/nr_hugepages &&
                     "$(cat /proc/sys/vm/nr_hugepages)" -eq 0 ]]; then

Also I suggest to add in-line comment to help understanding why nr_hugepages
sysfs needs change. Something like,

# nvme-cli may fail to allocate linear memory for rather large IO buffers.
# Increase nr_hugepages to allow nvme-cli to try the linear memory allocation
# from HugeTLB pool.

> +
>  	local dev="/dev/${nvmedev}n1"
>  	test_user_io "$dev" 1 512 > "$FULL" 2>&1 || echo FAIL
>  	test_user_io "$dev" 1 511 > "$FULL" 2>&1 || echo FAIL
> @@ -70,6 +76,10 @@ test() {
>  	test_user_io "$dev" 511 1023 > "$FULL" 2>&1 || echo FAIL
>  	test_user_io "$dev" 511 1025 > "$FULL" 2>&1 || echo FAIL
>  
> +	if [[ ${reset_nr_hugepages} = true ]]; then
> +		echo 0 > /proc/sys/vm/nr_hugepages
> +	fi
> +
>  	_nvme_disconnect_subsys "${def_subsysnqn}" >> "$FULL" 2>&1
>  
>  	_nvmet_target_cleanup
> -- 
> 2.43.1
>