memcg: remove v1 soft limit reclaim

Patch series "memcg: remove the v1 soft limit", v2.

The v1 soft limit was deprecated in v6.12 by commit 569c4f62d84a ("memcg:
initiate deprecation of v1 soft limit") and nobody has reported depending
on it in the ~21 months since.  memory.low and memory.min in v2 have
covered the same ground for far longer.

The knob has since been made inert by "memcg: make the v1 soft limit knob
inert", already queued in mm-hotfixes as a backportable fix for a syzbot
report [1].  Nothing can enter the soft limit rbtree anymore, so this
series just deletes the machinery that is now dead: the reclaim pass in
kswapd and direct reclaim, mem_cgroup_shrink_node() and its tracepoints,
the per-node rbtree, lru_gen_soft_reclaim() and the MEMCG_LRU_HEAD op, the
per-node tree fields, mem_cgroup->soft_limit, and finally the v1 event
ratelimiting which is now down to a single target.

memory.soft_limit_in_bytes itself is untouched: writes stay ignored and
reads keep returning the maximum value.


This patch (of 8):

Nothing can put a cgroup on the soft limit rbtree anymore, so the tree is
always empty and both callers of memcg1_soft_limit_reclaim() are
guaranteed no-ops.  Remove the reclaim pass from direct reclaim and from
kswapd, along with its implementation.

In shrink_zones() this leaves the global reclaim branch with a last_pgdat
check that is now redundant with the identical check right below it, so
drop it and move the explaining comment down to the check that remains. 
That check could only ever fire once last_pgdat was set, which implies
first_pgdat had already been assigned, so skipping it does not change
which node consider_reclaim_throttle() gets.

Link: https://lore.kernel.org/20260902174311.1772372-1-shakeel.butt@linux.dev
Link: https://lore.kernel.org/20260902174311.1772372-2-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: T.J. Mercier <tjmercier@google.com>

1 files changed, 0 insertions, 12 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index da625d2edb3b..11c1fa88d6fd 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1924,10 +1924,6 @@ static inline bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg)
 /* Cgroup v1-related declarations */
 
 #ifdef CONFIG_MEMCG_V1
-unsigned long memcg1_soft_limit_reclaim(pg_data_t *pgdat, int order,
-					gfp_t gfp_mask,
-					unsigned long *total_scanned);
-
 bool mem_cgroup_oom_synchronize(bool wait);
 
 static inline bool task_in_memcg_oom(struct task_struct *p)
@@ -1948,14 +1944,6 @@ static inline void mem_cgroup_exit_user_fault(void)
 }
 
 #else /* CONFIG_MEMCG_V1 */
-static inline
-unsigned long memcg1_soft_limit_reclaim(pg_data_t *pgdat, int order,
-					gfp_t gfp_mask,
-					unsigned long *total_scanned)
-{
-	return 0;
-}
-
 static inline bool task_in_memcg_oom(struct task_struct *p)
 {
 	return false;