Re: [PATCH] mm: memcontrol: move memsw charge callbacks to v1

Hugh Dickins
2025-01-24T06:53:17Z

On Fri, 24 Jan 2025, Johannes Weiner wrote:

> The interweaving of two entirely different swap accounting strategies
> has been one of the more confusing parts of the memcg code. Split out
> the v1 code to clarify the implementation and a handful of callsites,
> and to avoid building the v1 bits when !CONFIG_MEMCG_V1.
>
> text data bss dec hex filename
> 39253 6446 4160 49859 c2c3 mm/memcontrol.o.old
> 38877 6382 4160 49419 c10b mm/memcontrol.o
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

I'm not really looking at this, but want to chime in that I found the
memcg1 swap stuff in mm/memcontrol.c, not in mm/memcontrol-v1.c, very
misleading when I was doing the folio_unqueue_deferred_split() business:
so, without looking into the details of it, strongly approve of the
direction you're taking here - thank you.

But thought you could go even further, given that
static inline bool do_memsw_account(void)
{
return !cgroup_subsys_on_dfl(memory_cgrp_subsys);
}

I thought that amounted to do_memsw_account iff memcg_v1;
but I never did grasp cgroup_subsys_on_dfl very well,
so ignore me if I'm making no sense to you.

Hugh