Re: [PATCH v2 7/9] eal: add --in-memory option

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 13-Jul-18 1:13 PM, Thomas Monjalon wrote:
> 13/07/2018 12:27, Anatoly Burakov:
>> This command-line option will cause DPDK to operate entirely in
>> memory and not create any shared files at runtime, including any
>> shared configuration or hugetlbfs files. This is useful for debug
>> purposes, as well as for certain use cases like containers or
>> automatic memory cleanup.
>>
>> Currently, this option acts as a strict superset of --no-shconf and
>> --huge-unlink commands.
>>
>> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> 
> I would like to see some support or review for this feature.
> 

While the justification for it can be use-cases like running a DPDK 
process without worrying about cleaning up its hugepages afterwards 
(somewhat less of a concern since 18.05 but still a concern if primary 
crashes), it is really fixing the no-shconf/huge-unlink options to not 
be half-measures.

Both of these options effectively disable secondary processes, but don't 
do it in a consistent way - huge-unlink cleans up hugepages after 
allocating them, but leaves shared config on. No-shconf disables shared 
config, but leaves hugepages in place. Since 18.05, huge-unlink didn't 
work anyway (wasn't implemented, which was my omission), and due to EAL 
now relying on fbarray's to store some data, no-shconf wasn't working 
correctly either because even though shared config wasn't created, two 
primaries still couldn't share a prefix with --no-shconf (see the first 
patch).

So, this patchset is really an acknowledgement of the fact that both 
huge-unlink and no-shconf options are really there to disable secondary 
processes and stop leaving files on the file system. I just went one 
step further, and instead of allocating-and-then-removing hugepages 
we're not creating them in the first place, and map them anonymously 
instead.

-- 
Thanks,
Anatoly