Re: [PATCH v1 3/3] mm/damon/core: use node counters instead of flushing the root memcg

[SJ Park <sj@kernel.org>]

Hi Joanne,


On Mon,  2 Nov 2026 14:50:30 -0800 Joanne Koong <joannelkoong@gmail.com> wrote:

> damos_get_node_memcg_used_bp() flushes the memcg stats before reading
> the LRU sizes of the goal's memcg on the goal's node. For the root
> memcg, that flushes every cgroup in the system. The flush is not
> ratelimited, which means it happens every time the goal is evaluated.

Just thinking loudly.  damos_get_node_memcg_used_bp() is called only once per
DAMOS quota reset interval.  It is usually recommended to set the interval to 1
second.  So a sort of rate limiting is applied in common use cases.  That said,
some users might using quite short interval.  And it is obviously better to
avoid unnecessary flushes.

> 
> For the root memcg, the node counters hold the same LRU sizes as the
> memcg rstat stats, and they are always up to date. Use
> lruvec_lru_page_state(), which reads the node counters for the root
> memcg, and skip the flush for the root memcg.

Again, loud thought.  For root memcg, users might use
DAMOS_QUOTA_NODE_MEM_{USED,FREE}_BP instead, which calls
damos_get_node_mem_bp().  That said, some users might use
DAMOS_QUOTA_NODE_MEMCG_{USED,FREE}_BP for root memcg (maybe it makes user space
tool writing easier?).

So, looks all good to me, thank you for this patch.

> 
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>

Assuming the discussion on patch 2 concludes to have lruvec_lru_page_state(),

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

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