Re: [PATCH v3 26/30 fix] mm: mglru: do not call update_lru_size() during reparenting

[Harry Yoo]

On Wed, Jan 21, 2026 at 12:53:28PM +0900, Harry Yoo wrote:
> On Thu, Jan 15, 2026 at 06:44:44PM +0800, Qi Zheng wrote:
> > From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > 
> > Only non-hierarchical lruvec_stats->state_local needs to be reparented,
> > so handle it in reparent_state_local(), and remove the unreasonable
> > update_lru_size() call in __lru_gen_reparent_memcg().
> 
> Hmm well, how are the hierarchical statistics consistent when pages are
> reparented from an "active" gen to an "inactive" gen, or the other way around?
> 
> They'll become inconsistent when those pages are reclaimed or
> moved between generations?

FYI we've observed this while testing downstream implementation
as it led to MemAvailable being unreasonably high due to inconsistent
statistics.

The solution was, if lru_gen_is_active(child, gen) and
lru_gen_is_active(parent, gen) do not match, # of pages being
reparented must be subtracted from the child's statistics
(and up to the root, as it's hierarchical), and added to the parent's
statistics for the generation.

-- 
Cheers,
Harry / Hyeonggon