Re: Low TCP throughput due to vmpressure with swap enabled

On Wed, Dec 07, 2022 at 01:53:00PM +0100, Johannes Weiner wrote:
[...]

I don't mind doing that if necessary, but looking at the code I don't
see why it would be.

The socket code sets protocol memory pressure on allocations that run
into limits, and clears pressure on allocations that succeed and
frees. Why shouldn't we do the same thing for memcg?

I think you are right. Let's go with whatever you have for now as this
will reduce vmpressure dependency.

However I think there are still open issues that needs to be addressed
in the future:

1. Unlike TCP memory accounting, memcg has to account/charge user
memory, kernel memory and tcp/netmem. So, it might make more sense to
enter the pressure state in try_charge_memcg() function. This means
charging of user memory or kernel memory can also put the memcg under
socket pressure.

2. On RX path, the memcg charge can succeed due to GFP_ATOMIC flag.
Should we reset the pressure state in that case?

3. On uncharge path, unlike network stack, should we unconditionally
reset the socket pressure state?

Shakeel