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

[Damien Le Moal <dlemoal@kernel.org>]

On 2/21/24 16:37, Daniel Wagner wrote:
> On Wed, Feb 21, 2024 at 06:22:29AM +0000, Shinichiro Kawasaki wrote:
>> 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?
> 
> Obviously, we should aim for really solid test cases. Though it is not
> guaranteed that the test will pass even with CONFIG_HUGETLBS enabled. I
> suspect we would need to make some more preparation steps that the
> allocation has a high change to pass. Though I haven't really looked
> into what the necessary steps would be. The sysfs exposes a few more
> knobs to play with.

"echo 3 > /proc/sys/vm/drop_caches" before mounting hugetlbfs should allow for
the big pages to fit... Still no guarantees but likely that will lower setup
failure frequency.

> 
>> 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
> 
> Sure, I'll add this and also fix the typos in the commit message.
> 
>>
>> 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.
> 
> Ok.
> 

-- 
Damien Le Moal
Western Digital Research