Re: [PATCH 1/2] mm/vmscan: remove redundant !mem_cgroup_online() checks

[Johannes Weiner]

On Tue, Oct 27, 2026 at 06:06:05PM -0700, T.J. Mercier wrote:
> Since commit f1cf8d2f36dc ("mm: memcontrol: eliminate the problem of
> dying memory cgroup for LRU folios") and commit 0e0ac326c511 ("memcg:
> move LRU size accounting on reparenting instead of copying it"),
> mem_cgroup_css_offline() reparents all LRU folios to the parent memcg
> and zeroes the child's lrugen->nr_pages and lru_zone_size before the
> memcg is offlined. Nothing can repopulate the offlined memcg's lruvec
> afterwards. A folio that is off the LRU during reparenting looks up its
> lruvec through its objcg, which now points to the parent so it is put
> back on the parent's LRU.
> 
> As a result, lruvec_lru_size() and lruvec_evictable_size() are always 0
> when !mem_cgroup_online(memcg) is true, making the offlined memcg special
> cases in get_scan_count(), lruvec_is_sizable(), and shrink_one() dead
> code. Remove them.
> 
> With the get_nr_to_scan() special case removed, an offlined memcg that
> still has stale effective protection now has
> apply_proportional_protection() applied like get_scan_count() does, so
> the MGLRU and traditional LRU behavior is now the same.
> 
> Signed-off-by: T.J. Mercier <tjmercier@xxxxxxxxxx>

Great cleanup!

Reviewed-by: Johannes Weiner <hannes@xxxxxxxxxxx>