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mm: shrinker: add infrastructure for dynamically allocating shrinker
Patch series "use refcount+RCU method to implement lockless slab shrink", v6. 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/[email protected]/ [2]. https://lore.kernel.org/lkml/[email protected]/ [3]. https://lore.kernel.org/all/[email protected]/ [4]. https://lore.kernel.org/lkml/[email protected]/ 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 synchronize_rcu() when the module is unloaded. For case c, the memory of shrinker instance will be freed along with the structure it is embedded in. In preparation for implementing lockless slab shrink, we need to dynamically allocate those shrinker instances in case c, then the memory can be dynamically freed alone by calling kfree_rcu(). This patchset adds the following new APIs for dynamically allocating shrinker, and add a private_data field to struct shrinker to record and get the original embedded structure. 1. shrinker_alloc() 2. shrinker_register() 3. shrinker_free() In order to simplify shrinker-related APIs and make shrinker more independent of other kernel mechanisms, this patchset uses the above APIs to convert all shrinkers (including case a and b) to dynamically allocated, and then remove all existing APIs. This will also have another advantage mentioned by Dave Chinner: ``` The other advantage of this is that it will break all the existing out of tree code and third party modules using the old API and will no longer work with a kernel using lockless slab shrinkers. They need to break (both at the source and binary levels) to stop bad things from happening due to using uncoverted shrinkers in the new setup. ``` Then we free the shrinker by calling call_rcu(), and use rcu_read_{lock,unlock}() to ensure that the shrinker instance is valid. And 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: introduce new APIs PATCH 2~38: convert all shrinnkers to use new APIs PATCH 39: remove old APIs PATCH 40~41: some cleanups and preparations PATCH 42-43: implement the lockless slab shrink PATCH 44~45: convert shrinker_rwsem to mutex 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 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 $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs; mkdir -p $DIR/$i; done } do_mount() { for i in `seq $1 $2`; do mount -t tmpfs $i $DIR/$i; done } do_touch() { for i in `seq $1 $2`; do echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs; dd if=/dev/zero of=$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 1) Before applying this patchset: 33.15% [kernel] [k] down_read_trylock 25.38% [kernel] [k] shrink_slab 21.75% [kernel] [k] up_read 4.45% [kernel] [k] _find_next_bit 2.27% [kernel] [k] do_shrink_slab 1.80% [kernel] [k] intel_idle_irq 1.79% [kernel] [k] shrink_lruvec 0.67% [kernel] [k] xas_descend 0.41% [kernel] [k] mem_cgroup_iter 0.40% [kernel] [k] shrink_node 0.38% [kernel] [k] list_lru_count_one 2) After applying this patchset: 64.56% [kernel] [k] shrink_slab 12.18% [kernel] [k] do_shrink_slab 3.30% [kernel] [k] __rcu_read_unlock 2.61% [kernel] [k] shrink_lruvec 2.49% [kernel] [k] __rcu_read_lock 1.93% [kernel] [k] intel_idle_irq 0.89% [kernel] [k] shrink_node 0.81% [kernel] [k] mem_cgroup_iter 0.77% [kernel] [k] mem_cgroup_calculate_protection 0.66% [kernel] [k] list_lru_count_one We can see that the first perf hotspot becomes shrink_slab, which is what we expect. 3.2 registration and unregistration 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 473062 60.00 8.00 279.13 7884.12 1647.59 for a 60.01s run time: 1440.34s available CPU time 7.99s user time ( 0.55%) 279.13s system time ( 19.38%) 287.12s total time ( 19.93%) load average: 7.12 2.99 1.15 successful run completed in 60.01s (1 min, 0.01 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 477165 60.00 8.13 281.34 7952.55 1648.40 for a 60.01s run time: 1440.33s available CPU time 8.12s user time ( 0.56%) 281.34s system time ( 19.53%) 289.46s total time ( 20.10%) load average: 6.98 3.03 1.19 successful run completed in 60.01s (1 min, 0.01 secs) We can see that the ops/s has hardly changed. This patch (of 45): 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 synchronize_rcu() when the module is unloaded. For case c, the memory of shrinker instance will be freed along with the structure it is embedded in. In preparation for implementing lockless slab shrink, we need to dynamically allocate those shrinker instances in case c, then the memory can be dynamically freed alone by calling kfree_rcu(). So this commit adds the following new APIs for dynamically allocating shrinker, and add a private_data field to struct shrinker to record and get the original embedded structure. 1. shrinker_alloc() Used to allocate shrinker instance itself and related memory, it will return a pointer to the shrinker instance on success and NULL on failure. 2. shrinker_register() Used to register the shrinker instance, which is same as the current register_shrinker_prepared(). 3. shrinker_free() Used to unregister (if needed) and free the shrinker instance. In order to simplify shrinker-related APIs and make shrinker more independent of other kernel mechanisms, subsequent submissions will use the above API to convert all shrinkers (including case a and b) to dynamically allocated, and then remove all existing APIs. This will also have another advantage mentioned by Dave Chinner: ``` The other advantage of this is that it will break all the existing out of tree code and third party modules using the old API and will no longer work with a kernel using lockless slab shrinkers. They need to break (both at the source and binary levels) to stop bad things from happening due to using unconverted shrinkers in the new setup. ``` [[email protected]: mm: shrinker: some cleanup] Link: https://lkml.kernel.org/r/[email protected] Link: https://lkml.kernel.org/r/[email protected] Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Qi Zheng <[email protected]> Reviewed-by: Muchun Song <[email protected]> Cc: Christian Brauner <[email protected]> Cc: Chuck Lever <[email protected]> Cc: Darrick J. Wong <[email protected]> Cc: Dave Chinner <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: Kirill Tkhai <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Roman Gushchin <[email protected]> Cc: Sergey Senozhatsky <[email protected]> Cc: Steven Price <[email protected]> Cc: Theodore Ts'o <[email protected]> Cc: Vlastimil Babka <[email protected]> Cc: Abhinav Kumar <[email protected]> Cc: Alasdair Kergon <[email protected]> Cc: Alexander Viro <[email protected]> Cc: Alyssa Rosenzweig <[email protected]> Cc: Andreas Dilger <[email protected]> Cc: Andreas Gruenbacher <[email protected]> Cc: Anna Schumaker <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Bob Peterson <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Carlos Llamas <[email protected]> Cc: Chandan Babu R <[email protected]> Cc: Chao Yu <[email protected]> Cc: Chris Mason <[email protected]> Cc: Christian Koenig <[email protected]> Cc: Coly Li <[email protected]> Cc: Dai Ngo <[email protected]> Cc: Daniel Vetter <[email protected]> Cc: Daniel Vetter <[email protected]> Cc: Dave Hansen <[email protected]> Cc: David Airlie <[email protected]> Cc: David Hildenbrand <[email protected]> Cc: David Sterba <[email protected]> Cc: Dmitry Baryshkov <[email protected]> Cc: Gao Xiang <[email protected]> Cc: Huang Rui <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Jaegeuk Kim <[email protected]> Cc: Jani Nikula <[email protected]> Cc: Jan Kara <[email protected]> Cc: Jason Wang <[email protected]> Cc: Jeff Layton <[email protected]> Cc: Jeffle Xu <[email protected]> Cc: Joel Fernandes (Google) <[email protected]> Cc: Joonas Lahtinen <[email protected]> Cc: Josef Bacik <[email protected]> Cc: Juergen Gross <[email protected]> Cc: Kent Overstreet <[email protected]> Cc: Marijn Suijten <[email protected]> Cc: "Michael S. Tsirkin" <[email protected]> Cc: Mike Snitzer <[email protected]> Cc: Minchan Kim <[email protected]> Cc: Nadav Amit <[email protected]> Cc: Neil Brown <[email protected]> Cc: Oleksandr Tyshchenko <[email protected]> Cc: Olga Kornievskaia <[email protected]> Cc: Richard Weinberger <[email protected]> Cc: Rob Clark <[email protected]> Cc: Rob Herring <[email protected]> Cc: Rodrigo Vivi <[email protected]> Cc: Sean Paul <[email protected]> Cc: Song Liu <[email protected]> Cc: Stefano Stabellini <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Tomeu Vizoso <[email protected]> Cc: Tom Talpey <[email protected]> Cc: Trond Myklebust <[email protected]> Cc: Tvrtko Ursulin <[email protected]> Cc: Xuan Zhuo <[email protected]> Cc: Yue Hu <[email protected]> Signed-off-by: Andrew Morton <[email protected]>
This commit is contained in:
Qi Zheng
@@ -70,6 +70,8 @@ struct shrinker {
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int seeks; /* seeks to recreate an obj */
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unsigned flags;
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void *private_data;
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/* These are for internal use */
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struct list_head list;
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#ifdef CONFIG_MEMCG
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@@ -86,15 +88,22 @@ struct shrinker {
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};
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#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
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/* Flags */
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#define SHRINKER_REGISTERED (1 << 0)
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#define SHRINKER_NUMA_AWARE (1 << 1)
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#define SHRINKER_MEMCG_AWARE (1 << 2)
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/* Internal flags */
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#define SHRINKER_REGISTERED BIT(0)
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#define SHRINKER_ALLOCATED BIT(1)
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/* Flags for users to use */
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#define SHRINKER_NUMA_AWARE BIT(2)
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#define SHRINKER_MEMCG_AWARE BIT(3)
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/*
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* It just makes sense when the shrinker is also MEMCG_AWARE for now,
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* non-MEMCG_AWARE shrinker should not have this flag set.
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*/
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#define SHRINKER_NONSLAB (1 << 3)
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#define SHRINKER_NONSLAB BIT(4)
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struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...);
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void shrinker_register(struct shrinker *shrinker);
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void shrinker_free(struct shrinker *shrinker);
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extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker,
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const char *fmt, ...);
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@@ -1160,6 +1160,20 @@ unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
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int priority);
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#ifdef CONFIG_SHRINKER_DEBUG
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static inline int shrinker_debugfs_name_alloc(struct shrinker *shrinker,
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const char *fmt, va_list ap)
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{
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shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
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return shrinker->name ? 0 : -ENOMEM;
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}
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static inline void shrinker_debugfs_name_free(struct shrinker *shrinker)
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{
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kfree_const(shrinker->name);
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shrinker->name = NULL;
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}
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extern int shrinker_debugfs_add(struct shrinker *shrinker);
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extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
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int *debugfs_id);
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@@ -1170,6 +1184,14 @@ static inline int shrinker_debugfs_add(struct shrinker *shrinker)
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{
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return 0;
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}
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static inline int shrinker_debugfs_name_alloc(struct shrinker *shrinker,
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const char *fmt, va_list ap)
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{
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return 0;
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}
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static inline void shrinker_debugfs_name_free(struct shrinker *shrinker)
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{
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}
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static inline struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
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int *debugfs_id)
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{
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+106
@@ -550,6 +550,112 @@ out:
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return freed;
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}
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struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...)
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{
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struct shrinker *shrinker;
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unsigned int size;
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va_list ap;
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int err;
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shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL);
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if (!shrinker)
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return NULL;
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va_start(ap, fmt);
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err = shrinker_debugfs_name_alloc(shrinker, fmt, ap);
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va_end(ap);
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if (err)
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goto err_name;
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shrinker->flags = flags | SHRINKER_ALLOCATED;
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shrinker->seeks = DEFAULT_SEEKS;
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if (flags & SHRINKER_MEMCG_AWARE) {
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err = prealloc_memcg_shrinker(shrinker);
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if (err == -ENOSYS) {
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/* Memcg is not supported, fallback to non-memcg-aware shrinker. */
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shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
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goto non_memcg;
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}
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if (err)
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goto err_flags;
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return shrinker;
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}
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non_memcg:
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/*
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* The nr_deferred is available on per memcg level for memcg aware
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* shrinkers, so only allocate nr_deferred in the following cases:
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* - non-memcg-aware shrinkers
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* - !CONFIG_MEMCG
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* - memcg is disabled by kernel command line
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*/
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size = sizeof(*shrinker->nr_deferred);
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if (flags & SHRINKER_NUMA_AWARE)
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size *= nr_node_ids;
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shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
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if (!shrinker->nr_deferred)
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goto err_flags;
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return shrinker;
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err_flags:
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shrinker_debugfs_name_free(shrinker);
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err_name:
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kfree(shrinker);
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return NULL;
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}
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EXPORT_SYMBOL_GPL(shrinker_alloc);
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void shrinker_register(struct shrinker *shrinker)
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{
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if (unlikely(!(shrinker->flags & SHRINKER_ALLOCATED))) {
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pr_warn("Must use shrinker_alloc() to dynamically allocate the shrinker");
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return;
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}
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down_write(&shrinker_rwsem);
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list_add_tail(&shrinker->list, &shrinker_list);
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shrinker->flags |= SHRINKER_REGISTERED;
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shrinker_debugfs_add(shrinker);
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up_write(&shrinker_rwsem);
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}
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EXPORT_SYMBOL_GPL(shrinker_register);
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void shrinker_free(struct shrinker *shrinker)
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{
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struct dentry *debugfs_entry = NULL;
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int debugfs_id;
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if (!shrinker)
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return;
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down_write(&shrinker_rwsem);
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if (shrinker->flags & SHRINKER_REGISTERED) {
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list_del(&shrinker->list);
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debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
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shrinker->flags &= ~SHRINKER_REGISTERED;
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}
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shrinker_debugfs_name_free(shrinker);
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if (shrinker->flags & SHRINKER_MEMCG_AWARE)
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unregister_memcg_shrinker(shrinker);
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up_write(&shrinker_rwsem);
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if (debugfs_entry)
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shrinker_debugfs_remove(debugfs_entry, debugfs_id);
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kfree(shrinker->nr_deferred);
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shrinker->nr_deferred = NULL;
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kfree(shrinker);
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}
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EXPORT_SYMBOL_GPL(shrinker_free);
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/*
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* Add a shrinker callback to be called from the vm.
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*/
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@@ -241,9 +241,6 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
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lockdep_assert_held(&shrinker_rwsem);
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kfree_const(shrinker->name);
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shrinker->name = NULL;
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*debugfs_id = entry ? shrinker->debugfs_id : -1;
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shrinker->debugfs_entry = NULL;
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