From: Muchun Song Date: Tue, 21 Jun 2022 12:56:48 +0000 (+0800) Subject: mm: memcontrol: remove dead code and comments X-Git-Tag: maple_v12_fixes~50 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=24f2e66e879acf469aeae468eebccc6e0a35c5e0;p=users%2Fjedix%2Flinux-maple.git mm: memcontrol: remove dead code and comments Patch series "Use obj_cgroup APIs to charge the LRU pages", v6. With the following patchsets applied, all the kernel memory is charged with the new APIs of obj_cgroup: commit f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects instead of pages") commit b4e0b68fbd9d ("mm: memcontrol: use obj_cgroup APIs to charge kmem pages") But user memory allocations (LRU pages) pinning memcgs for a long time - it exists at a larger scale and is causing recurring problems in the real world: page cache doesn't get reclaimed for a long time, or is used by the second, third, fourth, ... instance of the same job that was restarted into a new cgroup every time. Unreclaimable dying cgroups pile up, waste memory, and make page reclaim very inefficient. We can convert LRU pages and most other raw memcg pins to the objcg direction to fix this problem, and then the LRU pages will not pin the memcgs. This patchset aims to make the LRU pages to drop the reference to memory cgroup by using the APIs of obj_cgroup. Finally, we can see that the number of the dying cgroups will not increase if we run the following test script. #!/bin/bash dd if=/dev/zero of=temp bs=4096 count=1 cat /proc/cgroups | grep memory for i in {0..2000} do mkdir /sys/fs/cgroup/memory/test$i echo $$ > /sys/fs/cgroup/memory/test$i/cgroup.procs cat temp >> log echo $$ > /sys/fs/cgroup/memory/cgroup.procs rmdir /sys/fs/cgroup/memory/test$i done cat /proc/cgroups | grep memory rm -f temp log This patch (of 11): Since no-hierarchy mode is deprecated after commit bef8620cd8e0 ("mm: memcg: deprecate the non-hierarchical mode") so parent_mem_cgroup() cannot return a NULL except root memcg, however, root memcg cannot be offline, so it is safe to drop the check of returned value of parent_mem_cgroup(). Remove those dead code. The comments in memcg_offline_kmem() above memcg_reparent_list_lrus() are out of date since commit 5abc1e37afa0 ("mm: list_lru: allocate list_lru_one only when needed") There is no ordering requirement between memcg_reparent_list_lrus() and memcg_reparent_objcgs(), so remove those outdated comments. Link: https://lkml.kernel.org/r/20220621125658.64935-1-songmuchun@bytedance.com Link: https://lkml.kernel.org/r/20220621125658.64935-2-songmuchun@bytedance.com Signed-off-by: Muchun Song Acked-by: Roman Gushchin Cc: Johannes Weiner Cc: Waiman Long Cc: Michal Hocko Cc: Shakeel Butt Cc: Xiongchun Duan Cc: Michal Koutný Signed-off-by: Andrew Morton --- diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 4d31ce55b1c0d..318d8880d62af 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -866,8 +866,7 @@ static inline struct mem_cgroup *lruvec_memcg(struct lruvec *lruvec) * parent_mem_cgroup - find the accounting parent of a memcg * @memcg: memcg whose parent to find * - * Returns the parent memcg, or NULL if this is the root or the memory - * controller is in legacy no-hierarchy mode. + * Returns the parent memcg, or NULL if this is the root. */ static inline struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 163492b9efa9f..fc706d6fc2658 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3684,17 +3684,7 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg) return; parent = parent_mem_cgroup(memcg); - if (!parent) - 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); } #else @@ -7195,8 +7185,6 @@ static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg) break; } memcg = parent_mem_cgroup(memcg); - if (!memcg) - memcg = root_mem_cgroup; } return memcg; } diff --git a/mm/vmscan.c b/mm/vmscan.c index 88fce64cfa961..b68b0216424d0 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -409,13 +409,9 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg) { int i, nid; long nr; - struct mem_cgroup *parent; + struct mem_cgroup *parent = parent_mem_cgroup(memcg); struct shrinker_info *child_info, *parent_info; - parent = parent_mem_cgroup(memcg); - if (!parent) - parent = root_mem_cgroup; - /* Prevent from concurrent shrinker_info expand */ down_read(&shrinker_rwsem); for_each_node(nid) {