Re: [PATCH v2 0/5] Statsfs: a new ram-based file sytem for Linux kernel statistics

[David Rientjes]

On Tue, 5 May 2020, Paolo Bonzini wrote:

> >>> Since this is becoming a generic API (good!!), maybe we can discuss
> >>> possible ways to optimize gathering of stats in mass?
> >> Sure, the idea of a binary format was considered from the beginning in
> >> [1], and it can be done either together with the current filesystem, or
> >> as a replacement via different mount options.
> > 
> > ASCII stats are not scalable. A binary format is definitely the way to go.
> 
> I am totally in favor of having a binary format, but it should be
> introduced as a separate series on top of this one---and preferably by
> someone who has already put some thought into the problem (which
> Emanuele and I have not, beyond ensuring that the statsfs concept and
> API is flexible enough).
> 

The concern is that once this series is merged then /sys/kernel/stats 
could be considered an ABI and there would be a reasonable expectation 
that it will remain stable, in so far as the stats that userspace is 
interested in are stable and not obsoleted.

So is this a suggestion that the binary format becomes complementary to 
statsfs and provide a means for getting all stats from a single subsystem, 
or that this series gets converted to such a format before it is merged?

> ASCII stats are necessary for quick userspace consumption and for
> backwards compatibility with KVM debugfs (which is not an ABI, but it's
> damn useful and should not be dropped without providing something as
> handy), so this is what this series starts from.
>