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".
Unified · Split
| @@ -22,6 +22,7 @@ · 21 unmodified lines | ||
| 22 | 22 | #include <linux/namei.h> |
| 23 | 23 | #include <linux/miscdevice.h> |
| 24 | 24 | #include <linux/magic.h> |
| 25 | +#include <linux/memcontrol.h> | |
| 25 | 26 | #include <linux/slab.h> |
| 26 | 27 | #include <linux/ratelimit.h> |
| 27 | 28 | #include <linux/crc32c.h> |
| @@ -2434,6 +2435,15 @@ static long btrfs_nr_cached_objects(struct super_block *sb, struct shrink_contro · 2406 unmodified lines | ||
| 2434 | 2435 | struct btrfs_fs_info *fs_info = btrfs_sb(sb); |
| 2435 | 2436 | const s64 nr = percpu_counter_read_positive(&fs_info->evictable_extent_maps); |
| 2436 | 2437 | |
| 2438 | + /* | |
| 2439 | + * The evictable extent map counter is filesystem-global and does not | |
| 2440 | + * honour sc->memcg, so it is only meaningful on the global (kswapd or | |
| 2441 | + * root direct reclaim) shrink path. Skip the per-memcg iterations of | |
| 2442 | + * shrink_slab_memcg() to avoid queueing duplicate global work. | |
| 2443 | + */ | |
| 2444 | + if (!mem_cgroup_shrink_is_root(sc)) | |
| 2445 | + return 0; | |
| 2446 | + | |
| 2437 | 2447 | trace_btrfs_extent_map_shrinker_count(fs_info, nr); |
| 2438 | 2448 | |
| 2439 | 2449 | return nr; |
| @@ -520,6 +520,22 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) · 519 unmodified lines | ||
| 520 | 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 | 539 | static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) |
| 524 | 540 | { |
| 525 | 541 | return objcg->is_root; |
| @@ -1071,6 +1087,11 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) · 545 unmodified lines | ||
| 1071 | 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 | 1095 | static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) |
| 1075 | 1096 | { |
| 1076 | 1097 | return true; |
| @@ -846,6 +846,16 @@ static long shmem_unused_huge_count(struct super_block *sb, · 845 unmodified lines | ||
| 846 | 846 | struct shrink_control *sc) |
| 847 | 847 | { |
| 848 | 848 | struct shmem_sb_info *sbinfo = SHMEM_SB(sb); |
| 849 | + | |
| 850 | + /* | |
| 851 | + * The per-superblock shrinklist is filesystem-global and does not | |
| 852 | + * honour sc->memcg, so it is only meaningful on the global (kswapd or | |
| 853 | + * root direct reclaim) shrink path. Skip the per-memcg iterations of | |
| 854 | + * shrink_slab_memcg() to avoid queueing duplicate global work. | |
| 855 | + */ | |
| 856 | + if (!mem_cgroup_shrink_is_root(sc)) | |
| 857 | + return 0; | |
| 858 | + | |
| 849 | 859 | return READ_ONCE(sbinfo->shrinklist_len); |
| 850 | 860 | } |
| 851 | 861 | #else /* !CONFIG_TRANSPARENT_HUGEPAGE */ |