Re: [PATCH nft] nft: memcg accounting for dynamically allocated objects

From: Florian Westphal
Date: Fri Apr 01 2022 - 15:32:05 EST

Vasily Averin <vasily.averin@xxxxxxxxx> wrote:
> > Same problem as connlimit, can be called from packet path.
> > Basically all GFP_ATOMIC are suspicious.
> >
> > Not sure how to resolve this, similar mechanics in iptables world (e.g.
> > connlimit or SET target) don't use memcg accounting.
> >
> > Perhaps for now resend with only the GFP_KERNEL parts converted?
> > Those are safe.
> It is safe for packet path too, _ACCOUNT allocation will not be able to find memcg
> in case of "!in_task()" context.
> On the other hand any additional checks on such path will affect performance.

I'm not sure this works with ksoftirqd serving network stack?

> Could you please estimate how often is this code used in the case of nft vs packet path?

It depends on user configuration.
Update from packet path is used for things like port knocking or other
dyanamic filter lists, or somehing like Limiting connections to x-per-address/subnet and so on.

> If the opposite is the case, then I can add __GFP_ACCOUNT flag depending on in_task() check.

But what task/memcg is used for the accounting in that case?