Re: How to estimate the upper bound of the peak memory consumption of cryptsetup itself?

On 24/06/2022 12:49, Coiby Xu wrote:
>>> Thanks for the reply! Sorry I meant the way to estimate the overhead of
>>> crypsetup itself i.e. ~256M in the above example. Previously I only take
>>> the memory consumption by memory-hard KDF into consideration and
>>> neglected the memory consumption of cryptsetup itself. This obviously
>>> leads to an underestimation of the memory requirement of cryptsetup. I
>>> need to overestimate the memory requirement a bit to make sure OOM won't
>>> happen that's why I am asking if there is a way to estimate the
>>> upper bound of memory requirement of cryptsetup itself.
>>
>> There is no generic way to get a number - it depends on configuration
>> of the distro, libc, translations, everything that is locked including
>> shared libraries.
>>
>> If it is about RHEL, you can perhaps know exact configuration - please
>> ask people in Red Hat.
> 
> Provided the configuration, is there an golden algorithm or a formula to
> get the number? If it doesn't exist and I need to do some tests to get
> an empirical number, are there any big factors I need to be aware of?

Think about current locales, OpenSSL policy and many other things.
(The major I remember was locking all libc loaded translations in memory.)

So really, the only answer here would be ... 42 :)

You can try to measure it. Not sure if it is reliable.

Usually people want to know this for some weird scenarios like kdump
or so - this is definitely not something upstream can help with.

Milan