Re: [External] Re: [PATCH] mm: vmscan: skip the file folios in proactive reclaim if swappiness is MAX

[Zhongkun He]

On Thu, Mar 13, 2025 at 7:17 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> On Wed, Mar 12, 2025 at 05:43:37PM +0800, Zhongkun He wrote:
> > With this patch 'commit <68cd9050d871> ("mm: add swappiness= arg to
> > memory.reclaim")', we can submit an additional swappiness=<val> argument
> > to memory.reclaim. It is very useful because we can dynamically adjust
> > the reclamation ratio based on the anonymous folios and file folios of
> > each cgroup. For example,when swappiness is set to 0, we only reclaim
> > from file pages.
> >
> > However,we have also encountered a new issue: when swappiness is set to
> > the MAX_SWAPPINESS, it may still only reclaim file folios. This is due
> > to the knob of cache_trim_mode, which depends solely on the ratio of
> > inactive folios, regardless of whether there are a large number of cold
> > folios in anonymous folio list.
> >
> > So, we hope to add a new control logic where proactive memory reclaim only
> > reclaims from anonymous folios when swappiness is set to MAX_SWAPPINESS.
> > For example, something like this:
> >
> > echo "2M swappiness=200" > /sys/fs/cgroup/memory.reclaim
> >
> > will perform reclaim on the rootcg with a swappiness setting of 200 (max
> > swappiness) regardless of the file folios. Users have a more comprehensive
> > view of the application's memory distribution because there are many
> > metrics available.
>
> I'm not opposed but can you be a bit more specific on your usecase?
>
> Presumably this is with zram/zswap, where the IO tradeoff that
> cache_trim_mode is making doesn't hold - file refaults will cause IO,
> whereas anon decompression will not.

Indeed, I will add this description in the comments.

>
> > With this patch, the swappiness argument of memory.reclaim has a more
> > precise semantics: 0 means reclaiming only from file pages, while 200
> > means reclaiming just from anonymous pages.
> >
> > Signed-off-by: Zhongkun He <hezhongkun.hzk@xxxxxxxxxxxxx>
>
> Makes sense to me. With the doc update Andrew had asked for,
>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Got it, thanks.