Re: [PATCH V4 1/4] mm: add swappiness=max arg to memory.reclaim for only anon reclaim

[Muchun Song <muchun.song@linux.dev>]

> On Apr 21, 2025, at 17:13, Zhongkun He <hezhongkun.hzk@bytedance.com> 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 folios.
> 
> However,we have also encountered a new issue: when swappiness is set to
> the MAX_SWAPPINESS, it may still only reclaim file folios.
> 
> So, we hope to add a new arg 'swappiness=max' in memory.reclaim where
> proactive memory reclaim only reclaims from anonymous folios when
> swappiness is set to max. The swappiness semantics from a user
> perspective remain unchanged.
> 
> For example, something like this:
> 
> echo "2M swappiness=max" > /sys/fs/cgroup/memory.reclaim

We already have this kind of style (mixing numbers and strings) within
io.max under cgroup v2. As a result, I'm okay with this change. 

> 
> will perform reclaim on the rootcg with a swappiness setting of 'max' (a
> new mode) regardless of the file folios. Users have a more comprehensive
> view of the application's memory distribution because there are many
> metrics available. For example, if we find that a certain cgroup has a
> large number of inactive anon folios, we can reclaim only those and skip
> file folios, because with the zram/zswap, the IO tradeoff that
> cache_trim_mode or other file first logic is making doesn't hold -
> file refaults will cause IO, whereas anon decompression will not.
> 
> With this patch, the swappiness argument of memory.reclaim has a new
> mode 'max', means reclaiming just from anonymous folios both in traditional
> LRU and MGLRU.
> 
> Here is the previous discussion:
> https://lore.kernel.org/all/20250314033350.1156370-1-hezhongkun.hzk@bytedance.com/
> https://lore.kernel.org/all/20250312094337.2296278-1-hezhongkun.hzk@bytedance.com/
> https://lore.kernel.org/all/20250318135330.3358345-1-hezhongkun.hzk@bytedance.com/
> 
> Suggested-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>

Acked-by: Muchun Song <muchun.song@linux.dev>

Thanks.