Re: [PATCH V4 2/2] mm: add swapiness= arg to memory.reclaim

[Michal Hocko <mhocko@suse.com>]

On Thu 14-12-23 13:22:29, Dan Schatzberg wrote:
> On Thu, Dec 14, 2023 at 09:38:55AM +0100, Michal Hocko wrote:
[...]
> > While the review can point those out it is quite easy to break and you
> > will only learn about that very indirectly. I think it would be easier
> > to review and maintain if you go with a pointer that would fallback to
> > mem_cgroup_swappiness() if NULL which will be the case for every
> > existing reclaimer except memory.reclaim with swappiness value.
> 
> I agree. My initial implementation used a pointer for this
> reason. I'll switch this back. Just to be clear - I still need to
> initialize scan_control.swappiness in all these other places right?

No. They will just get initialized to 0. All you need to make sure is
that the swappiness is used consistently. I would propose something like
scan_control_swappiness() (or sc_swappiness) which would actually do

	if (sc->swappiness)
		return sc->swappiness;
	return mem_cgroup_swappiness(sc->target_mem_cgroup);

and then make sure that mem_cgroup_swappiness is never used directly.

-- 
Michal Hocko
SUSE Labs