Re: [PATCH v8 1/6] list_lru: allows explicit memcg and NUMA node selection

[Nhat Pham]

On Thu, Nov 30, 2023 at 11:57 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Thu, Nov 30, 2023 at 11:40:18AM -0800, Nhat Pham wrote:
> > This patch changes list_lru interface so that the caller must explicitly
> > specify numa node and memcg when adding and removing objects. The old
> > list_lru_add() and list_lru_del() are renamed to list_lru_add_obj() and
> > list_lru_del_obj(), respectively.
>
> Wouldn't it be better to add list_lru_add_memcg() and
> list_lru_del_memcg() and have:
>
> +bool list_lru_del(struct list_lru *lru, struct list_head *item)
> +{
> +       int nid = page_to_nid(virt_to_page(item));
> +       struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ?
> +               mem_cgroup_from_slab_obj(item) : NULL;
> +
> +       return list_lru_del_memcg(lru, item, nid, memcg);
> +}
>
> Seems like _most_ callers will want the original versions and only
> a few will want the explicit memcg/nid versions.  No?
>

I actually did something along that line in earlier iterations of this
patch series (albeit with poorer naming - __list_lru_add() instead of
list_lru_add_memcg()). The consensus after some back and forth was
that the original list_lru_add() was not a very good design (the
better one was this new version that allows for explicit numa/memcg
selection). So I agreed to fix it everywhere as a prep patch.

I don't have strong opinions here to be completely honest, but I do
think this new API makes more sense (at the cost of quite a bit of
elbow grease to fix every callsites and extra reviewing).