Commit 0baad6f9b997 ("fs/super: skip non-memcg-aware nr_cached_objects in memcg slab shrink") added a check in fs/super.c that skipped every ->nr_cached_objects() hook whenever the shrinker was invoked for a non-root memcg, on the assumption that none of them honour sc->memcg. That assumption is wrong for XFS, whose inode-reclaim hook is intentionally driven from per-memcg contexts to free memcg-charged slab. Encoding a blanket "never memcg-aware" policy in fs/super.c short-circuits that path. Push the check down into the callbacks whose counters really are irrelevant to per-memcg reclaim - btrfs_nr_cached_objects() and shmem_unused_huge_count() - and drop the fs/super.c gate. Each filesystem can now lift the restriction independently if its counter later grows memcg awareness, without touching fs/super.c. Introduce mem_cgroup_shrink_is_root() in <linux/memcontrol.h> so the callbacks don't open-code "sc->memcg is NULL or root".
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| @@ -520,6 +520,22 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) · 519 unmodified lines | |||
| 520 | return (memcg == root_mem_cgroup); | 520 | return (memcg == root_mem_cgroup); |
| 521 | } | 521 | } |
| 522 | 522 | ||
| 523 | /** | ||
| 524 | * mem_cgroup_shrink_is_root - is this a global or root-memcg shrink invocation? | ||
| 525 | * @sc: shrink_control describing the current shrinker call | ||
| 526 | * | ||
| 527 | * Returns true when @sc represents a global reclaim shrink (sc->memcg == NULL) | ||
| 528 | * or a root-memcg shrink, i.e. not a per-memcg iteration of | ||
| 529 | * shrink_slab_memcg(). Filesystems whose ->nr_cached_objects()/ | ||
| 530 | * ->free_cached_objects() implementations operate on filesystem-global state | ||
| 531 | * and do not honour sc->memcg can use this to early-return 0 in per-memcg | ||
| 532 | * contexts. | ||
| 533 | */ | ||
| 534 | static inline bool mem_cgroup_shrink_is_root(struct shrink_control *sc) | ||
| 535 | { | ||
| 536 | return !sc->memcg || mem_cgroup_is_root(sc->memcg); | ||
| 537 | } | ||
| 538 | |||
| 523 | static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) | 539 | static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) |
| 524 | { | 540 | { |
| 525 | return objcg->is_root; | 541 | return objcg->is_root; |
| @@ -1071,6 +1087,11 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) · 545 unmodified lines | |||
| 1071 | return true; | 1087 | return true; |
| 1072 | } | 1088 | } |
| 1073 | 1089 | ||
| 1090 | static inline bool mem_cgroup_shrink_is_root(struct shrink_control *sc) | ||
| 1091 | { | ||
| 1092 | return true; | ||
| 1093 | } | ||
| 1094 | |||
| 1074 | static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) | 1095 | static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) |
| 1075 | { | 1096 | { |
| 1076 | return true; | 1097 | return true; |