From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> Hi all, 1. Background ============= We used to implement the lockless slab shrink with SRCU [1], but then kernel test robot reported -88.8% regression in stress-ng.ramfs.ops_per_sec test case [2], so we reverted it [3]. This patch series aims to re-implement the lockless slab shrink using the refcount+RCU method proposed by Dave Chinner [4]. [1]. https://lore.kernel.org/lkml/20230313112819.38938-1-zhengqi.arch@xxxxxxxxxxxxx/ [2]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@xxxxxxxxx/ [3]. https://lore.kernel.org/all/20230609081518.3039120-1-qi.zheng@xxxxxxxxx/ [4]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@xxxxxxxxxxxxxxxxxxx/ 2. Implementation ================= Currently, the shrinker instances can be divided into the following three types: a) global shrinker instance statically defined in the kernel, such as workingset_shadow_shrinker. b) global shrinker instance statically defined in the kernel modules, such as mmu_shrinker in x86. c) shrinker instance embedded in other structures. For *case a*, the memory of shrinker instance is never freed. For *case b*, the memory of shrinker instance will be freed after the module is unloaded. But we will call synchronize_rcu() in free_module() to wait for RCU read-side critical section to exit. For *case c*, we need to dynamically allocate these shrinker instances, then the memory of shrinker instance can be dynamically freed alone by calling kfree_rcu(). Then we can use rcu_read_{lock,unlock}() to ensure that the shrinker instance is valid. The shrinker::refcount mechanism ensures that the shrinker instance will not be run again after unregistration. So the structure that records the pointer of shrinker instance can be safely freed without waiting for the RCU read-side critical section. In this way, while we implement the lockless slab shrink, we don't need to be blocked in unregister_shrinker() to wait RCU read-side critical section. PATCH 1 ~ 2: infrastructure for dynamically allocating shrinker instances PATCH 3 ~ 21: dynamically allocate the shrinker instances in case c PATCH 22: introduce pool_shrink_rwsem to implement private synchronize_shrinkers() PATCH 23 ~ 28: implement the lockless slab shrink PATCH 29: move shrinker-related code into a separate file 3. Testing ========== 3.1 slab shrink stress test --------------------------- We can reproduce the down_read_trylock() hotspot through the following script: ``` DIR="/root/shrinker/memcg/mnt" do_create() { mkdir -p /sys/fs/cgroup/memory/test mkdir -p /sys/fs/cgroup/perf_event/test echo 4G > /sys/fs/cgroup/memory/test/memory.limit_in_bytes for i in `seq 0 $1`; do mkdir -p /sys/fs/cgroup/memory/test/$i; echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs; echo $$ > /sys/fs/cgroup/perf_event/test/cgroup.procs; mkdir -p $DIR/$i; done } do_mount() { for i in `seq $1 $2`; do mount -t tmpfs $i $DIR/$i; done } do_touch() { for i in `seq $1 $2`; do echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs; echo $$ > /sys/fs/cgroup/perf_event/test/cgroup.procs; dd if=/dev/zero of=$DIR/$i/file$i bs=1M count=1 & done } case "$1" in touch) do_touch $2 $3 ;; test) do_create 4000 do_mount 0 4000 do_touch 0 3000 ;; *) exit 1 ;; esac ``` Save the above script, then run test and touch commands. Then we can use the following perf command to view hotspots: perf top -U -F 999 [-g] 1) Before applying this patchset: 35.34% [kernel] [k] down_read_trylock 18.44% [kernel] [k] shrink_slab 15.98% [kernel] [k] pv_native_safe_halt 15.08% [kernel] [k] up_read 5.33% [kernel] [k] idr_find 2.71% [kernel] [k] _find_next_bit 2.21% [kernel] [k] shrink_node 1.29% [kernel] [k] shrink_lruvec 0.66% [kernel] [k] do_shrink_slab 0.33% [kernel] [k] list_lru_count_one 0.33% [kernel] [k] __radix_tree_lookup 0.25% [kernel] [k] mem_cgroup_iter - 82.19% 19.49% [kernel] [k] shrink_slab - 62.00% shrink_slab 36.37% down_read_trylock 15.52% up_read 5.48% idr_find 3.38% _find_next_bit + 0.98% do_shrink_slab 2) After applying this patchset: 46.83% [kernel] [k] shrink_slab 20.52% [kernel] [k] pv_native_safe_halt 8.85% [kernel] [k] do_shrink_slab 7.71% [kernel] [k] _find_next_bit 1.72% [kernel] [k] xas_descend 1.70% [kernel] [k] shrink_node 1.44% [kernel] [k] shrink_lruvec 1.43% [kernel] [k] mem_cgroup_iter 1.28% [kernel] [k] xas_load 0.89% [kernel] [k] super_cache_count 0.84% [kernel] [k] xas_start 0.66% [kernel] [k] list_lru_count_one - 65.50% 40.44% [kernel] [k] shrink_slab - 22.96% shrink_slab 13.11% _find_next_bit - 9.91% do_shrink_slab - 1.59% super_cache_count 0.92% list_lru_count_one We can see that the first perf hotspot becomes shrink_slab, which is what we expect. 3.2 registeration and unregisteration stress test ------------------------------------------------- Run the command below to test: stress-ng --timeout 60 --times --verify --metrics-brief --ramfs 9 & 1) Before applying this patchset: setting to a 60 second run per stressor dispatching hogs: 9 ramfs stressor bogo ops real time usr time sys time bogo ops/s bogo ops/s (secs) (secs) (secs) (real time) (usr+sys time) ramfs 880623 60.02 7.71 226.93 14671.45 3753.09 ramfs: 1 System Management Interrupt for a 60.03s run time: 5762.40s available CPU time 7.71s user time ( 0.13%) 226.93s system time ( 3.94%) 234.64s total time ( 4.07%) load average: 8.54 3.06 2.11 passed: 9: ramfs (9) failed: 0 skipped: 0 successful run completed in 60.03s (1 min, 0.03 secs) 2) After applying this patchset: setting to a 60 second run per stressor dispatching hogs: 9 ramfs stressor bogo ops real time usr time sys time bogo ops/s bogo ops/s (secs) (secs) (secs) (real time) (usr+sys time) ramfs 847562 60.02 7.44 230.22 14120.66 3566.23 ramfs: 4 System Management Interrupts for a 60.12s run time: 5771.95s available CPU time 7.44s user time ( 0.13%) 230.22s system time ( 3.99%) 237.66s total time ( 4.12%) load average: 8.18 2.43 0.84 passed: 9: ramfs (9) failed: 0 skipped: 0 successful run completed in 60.12s (1 min, 0.12 secs) We can see that the ops/s has hardly changed. This series is based on next-20230613. Comments and suggestions are welcome. Thanks, Qi. Qi Zheng (29): mm: shrinker: add shrinker::private_data field mm: vmscan: introduce some helpers for dynamically allocating shrinker drm/i915: dynamically allocate the i915_gem_mm shrinker drm/msm: dynamically allocate the drm-msm_gem shrinker drm/panfrost: dynamically allocate the drm-panfrost shrinker dm: dynamically allocate the dm-bufio shrinker dm zoned: dynamically allocate the dm-zoned-meta shrinker md/raid5: dynamically allocate the md-raid5 shrinker bcache: dynamically allocate the md-bcache shrinker vmw_balloon: dynamically allocate the vmw-balloon shrinker virtio_balloon: dynamically allocate the virtio-balloon shrinker mbcache: dynamically allocate the mbcache shrinker ext4: dynamically allocate the ext4-es shrinker jbd2,ext4: dynamically allocate the jbd2-journal shrinker NFSD: dynamically allocate the nfsd-client shrinker NFSD: dynamically allocate the nfsd-reply shrinker xfs: dynamically allocate the xfs-buf shrinker xfs: dynamically allocate the xfs-inodegc shrinker xfs: dynamically allocate the xfs-qm shrinker zsmalloc: dynamically allocate the mm-zspool shrinker fs: super: dynamically allocate the s_shrink drm/ttm: introduce pool_shrink_rwsem mm: shrinker: add refcount and completion_wait fields mm: vmscan: make global slab shrink lockless mm: vmscan: make memcg slab shrink lockless mm: shrinker: make count and scan in shrinker debugfs lockless mm: vmscan: hold write lock to reparent shrinker nr_deferred mm: shrinkers: convert shrinker_rwsem to mutex mm: shrinker: move shrinker-related code into a separate file drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 27 +- drivers/gpu/drm/i915/i915_drv.h | 3 +- drivers/gpu/drm/msm/msm_drv.h | 2 +- drivers/gpu/drm/msm/msm_gem_shrinker.c | 25 +- drivers/gpu/drm/panfrost/panfrost_device.h | 2 +- .../gpu/drm/panfrost/panfrost_gem_shrinker.c | 24 +- drivers/gpu/drm/ttm/ttm_pool.c | 15 + drivers/md/bcache/bcache.h | 2 +- drivers/md/bcache/btree.c | 23 +- drivers/md/bcache/sysfs.c | 2 +- drivers/md/dm-bufio.c | 23 +- drivers/md/dm-cache-metadata.c | 2 +- drivers/md/dm-thin-metadata.c | 2 +- drivers/md/dm-zoned-metadata.c | 25 +- drivers/md/raid5.c | 28 +- drivers/md/raid5.h | 2 +- drivers/misc/vmw_balloon.c | 16 +- drivers/virtio/virtio_balloon.c | 26 +- fs/btrfs/super.c | 2 +- fs/ext4/ext4.h | 2 +- fs/ext4/extents_status.c | 21 +- fs/jbd2/journal.c | 32 +- fs/kernfs/mount.c | 2 +- fs/mbcache.c | 39 +- fs/nfsd/netns.h | 4 +- fs/nfsd/nfs4state.c | 20 +- fs/nfsd/nfscache.c | 33 +- fs/proc/root.c | 2 +- fs/super.c | 40 +- fs/xfs/xfs_buf.c | 25 +- fs/xfs/xfs_buf.h | 2 +- fs/xfs/xfs_icache.c | 27 +- fs/xfs/xfs_mount.c | 4 +- fs/xfs/xfs_mount.h | 2 +- fs/xfs/xfs_qm.c | 24 +- fs/xfs/xfs_qm.h | 2 +- include/linux/fs.h | 2 +- include/linux/jbd2.h | 2 +- include/linux/shrinker.h | 35 +- mm/Makefile | 4 +- mm/shrinker.c | 750 ++++++++++++++++++ mm/shrinker_debug.c | 26 +- mm/vmscan.c | 702 ---------------- mm/zsmalloc.c | 28 +- 44 files changed, 1128 insertions(+), 953 deletions(-) create mode 100644 mm/shrinker.c -- 2.30.2
