Re: [PATCH v3 1/5] mm/memcg: Pass both memcg and lruvec to mod_memcg_lruvec_state()

[Johannes Weiner]

On Tue, Apr 13, 2021 at 09:20:23PM -0400, Waiman Long wrote:
> The caller of mod_memcg_lruvec_state() has both memcg and lruvec readily
> available. So both of them are now passed to mod_memcg_lruvec_state()
> and __mod_memcg_lruvec_state(). The __mod_memcg_lruvec_state() is
> updated to allow either of the two parameters to be set to null. This
> makes mod_memcg_lruvec_state() equivalent to mod_memcg_state() if lruvec
> is null.
> 
> The new __mod_memcg_lruvec_state() function will be used in the next
> patch as a replacement of mod_memcg_state() in mm/percpu.c for the
> consolidation of the memory uncharge and vmstat update functions in
> the kmem_cache_free() path.

This requires users who want both to pass a pgdat that can be derived
from the lruvec. This is error prone, and we just acked a patch that
removes this very thing from mem_cgroup_page_lruvec().

With the suggestion for patch 2, this shouldn't be necessary anymore,
though. And sort of underlines my point around that combined function
creating akwward code above and below it.