The patch titled
Subject: mm/list_lru: code clean up for reparenting
has been added to the -mm mm-unstable branch. Its filename is
mm-list_lru-code-clean-up-for-reparenting.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-list_lru-code-clean-up-for-reparenting.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Kairui Song <kasong@xxxxxxxxxxx>
Subject: mm/list_lru: code clean up for reparenting
Date: Thu, 26 Sep 2024 01:10:17 +0800
No feature change, just change of code structure and fix comment.
The list lrus are not empty until memcg_reparent_list_lru_node() calls are
all done, so the comments in memcg_offline_kmem were slightly inaccurate.
Link: https://lkml.kernel.org/r/20240925171020.32142-4-ryncsn@xxxxxxxxx
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
Reviewed-by: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/list_lru.c | 39 +++++++++++++++++----------------------
mm/memcontrol.c | 7 -------
2 files changed, 17 insertions(+), 29 deletions(-)
--- a/mm/list_lru.c~mm-list_lru-code-clean-up-for-reparenting
+++ a/mm/list_lru.c
@@ -421,35 +421,16 @@ out:
spin_unlock_irq(&nlru->lock);
}
-static void memcg_reparent_list_lru(struct list_lru *lru,
- int src_idx, struct mem_cgroup *dst_memcg)
-{
- int i;
-
- for_each_node(i)
- memcg_reparent_list_lru_node(lru, i, src_idx, dst_memcg);
-
- memcg_list_lru_free(lru, src_idx);
-}
-
void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *parent)
{
struct cgroup_subsys_state *css;
struct list_lru *lru;
- int src_idx = memcg->kmemcg_id;
+ int src_idx = memcg->kmemcg_id, i;
/*
* Change kmemcg_id of this cgroup and all its descendants to the
* parent's id, and then move all entries from this cgroup's list_lrus
* to ones of the parent.
- *
- * After we have finished, all list_lrus corresponding to this cgroup
- * are guaranteed to remain empty. So we can safely free this cgroup's
- * list lrus in memcg_list_lru_free().
- *
- * Changing ->kmemcg_id to the parent can prevent memcg_list_lru_alloc()
- * from allocating list lrus for this cgroup after memcg_list_lru_free()
- * call.
*/
rcu_read_lock();
css_for_each_descendant_pre(css, &memcg->css) {
@@ -460,9 +441,23 @@ void memcg_reparent_list_lrus(struct mem
}
rcu_read_unlock();
+ /*
+ * With kmemcg_id set to parent, holding the lock of each list_lru_node
+ * below can prevent list_lru_{add,del,isolate} from touching the lru,
+ * safe to reparent.
+ */
mutex_lock(&list_lrus_mutex);
- list_for_each_entry(lru, &memcg_list_lrus, list)
- memcg_reparent_list_lru(lru, src_idx, parent);
+ list_for_each_entry(lru, &memcg_list_lrus, list) {
+ for_each_node(i)
+ memcg_reparent_list_lru_node(lru, i, src_idx, parent);
+
+ /*
+ * Here all list_lrus corresponding to the cgroup are guaranteed
+ * to remain empty, we can safely free this lru, any further
+ * memcg_list_lru_alloc() call will simply bail out.
+ */
+ memcg_list_lru_free(lru, src_idx);
+ }
mutex_unlock(&list_lrus_mutex);
}
--- a/mm/memcontrol.c~mm-list_lru-code-clean-up-for-reparenting
+++ a/mm/memcontrol.c
@@ -3101,13 +3101,6 @@ static void memcg_offline_kmem(struct me
parent = root_mem_cgroup;
memcg_reparent_objcgs(memcg, parent);
-
- /*
- * After we have finished memcg_reparent_objcgs(), all list_lrus
- * corresponding to this cgroup are guaranteed to remain empty.
- * The ordering is imposed by list_lru_node->lock taken by
- * memcg_reparent_list_lrus().
- */
memcg_reparent_list_lrus(memcg, parent);
}
_
Patches currently in -mm which might be from kasong@xxxxxxxxxxx are
mm-list_lru-dont-pass-unnecessary-key-parameters.patch
mm-list_lru-dont-export-list_lru_add.patch
mm-list_lru-code-clean-up-for-reparenting.patch
mm-list_lru-simplify-reparenting-and-initial-allocation.patch
mm-list_lru-split-the-lock-to-per-cgroup-scope.patch
mm-list_lru-simplify-the-list_lru-walk-callback-function.patch
