| Message ID | 20230724094354.90817-4-zhengqi.arch@bytedance.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | use refcount+RCU method to implement lockless slab shrink | expand |
On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote: > +void shrinker_unregister(struct shrinker *shrinker) > +{ > + struct dentry *debugfs_entry; > + int debugfs_id; > + > + if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED)) > + return; > + > + down_write(&shrinker_rwsem); > + list_del(&shrinker->list); > + shrinker->flags &= ~SHRINKER_REGISTERED; > + if (shrinker->flags & SHRINKER_MEMCG_AWARE) > + unregister_memcg_shrinker(shrinker); > + debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); > + up_write(&shrinker_rwsem); > + > + shrinker_debugfs_remove(debugfs_entry, debugfs_id); Should there not be an rcu_barrier() right about here? > + > + kfree(shrinker->nr_deferred); > + shrinker->nr_deferred = NULL; > + > + kfree(shrinker); > +} > +EXPORT_SYMBOL(shrinker_unregister);
Hi Peter, On 2023/7/24 20:25, Peter Zijlstra wrote: > On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote: > >> +void shrinker_unregister(struct shrinker *shrinker) >> +{ >> + struct dentry *debugfs_entry; >> + int debugfs_id; >> + >> + if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED)) >> + return; >> + >> + down_write(&shrinker_rwsem); >> + list_del(&shrinker->list); >> + shrinker->flags &= ~SHRINKER_REGISTERED; >> + if (shrinker->flags & SHRINKER_MEMCG_AWARE) >> + unregister_memcg_shrinker(shrinker); >> + debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); >> + up_write(&shrinker_rwsem); >> + >> + shrinker_debugfs_remove(debugfs_entry, debugfs_id); > > Should there not be an rcu_barrier() right about here? The shrinker_debugfs_remove() will wait for debugfs_file_put() to return, so when running here, all shrinker debugfs operations have been completed. And the slab shrink will hold the read lock of shrinker_rwsem to traverse the shrinker_list, so when we hold the write lock of shrinker_rwsem to delete the shrinker from the shrinker_list, the shrinker will not be executed again. So I think there is no need to add a rcu_barrier() here. Please let me know if I missed something. Thanks, Qi > >> + >> + kfree(shrinker->nr_deferred); >> + shrinker->nr_deferred = NULL; >> + >> + kfree(shrinker); >> +} >> +EXPORT_SYMBOL(shrinker_unregister); >
On 2023/7/24 17:43, Qi Zheng wrote: > 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_free_non_registered() > > Used to destroy the non-registered shrinker instance. At least I don't like this name. I know you want to tell others this function only should be called when shrinker has not been registed but allocated. Maybe shrinker_free() is more simple. And and a comment to tell the users when to use it. > > 3. shrinker_register() > > Used to register the shrinker instance, which is same as the current > register_shrinker_prepared(). > > 4. shrinker_unregister() > > Used to unregister 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 uncoverted shrinkers in the new > setup. > ``` > > Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> > --- > include/linux/shrinker.h | 6 +++ > mm/shrinker.c | 113 +++++++++++++++++++++++++++++++++++++++ > 2 files changed, 119 insertions(+) > > diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h > index 961cb84e51f5..296f5e163861 100644 > --- a/include/linux/shrinker.h > +++ b/include/linux/shrinker.h > @@ -70,6 +70,8 @@ struct shrinker { > int seeks; /* seeks to recreate an obj */ > unsigned flags; > > + void *private_data; > + > /* These are for internal use */ > struct list_head list; > #ifdef CONFIG_MEMCG > @@ -98,6 +100,10 @@ struct shrinker { > > unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg, > int priority); > +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...); > +void shrinker_free_non_registered(struct shrinker *shrinker); > +void shrinker_register(struct shrinker *shrinker); > +void shrinker_unregister(struct shrinker *shrinker); > > extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker, > const char *fmt, ...); > diff --git a/mm/shrinker.c b/mm/shrinker.c > index 0a32ef42f2a7..d820e4cc5806 100644 > --- a/mm/shrinker.c > +++ b/mm/shrinker.c > @@ -548,6 +548,119 @@ unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg, > return freed; > } > > +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...) > +{ > + struct shrinker *shrinker; > + unsigned int size; > + va_list __maybe_unused ap; > + int err; > + > + shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL); > + if (!shrinker) > + return NULL; > + > +#ifdef CONFIG_SHRINKER_DEBUG > + va_start(ap, fmt); > + shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap); > + va_end(ap); > + if (!shrinker->name) > + goto err_name; > +#endif So why not introduce another helper to handle this and declare it as a void function when !CONFIG_SHRINKER_DEBUG? Something like the following: #ifdef CONFIG_SHRINKER_DEBUG static int shrinker_debugfs_name_alloc(struct shrinker *shrinker, const char *fmt, va_list vargs) { shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, vargs); return shrinker->name ? 0 : -ENOMEM; } #else static int shrinker_debugfs_name_alloc(struct shrinker *shrinker, const char *fmt, va_list vargs) { return 0; } #endif > + shrinker->flags = flags; > + > + if (flags & SHRINKER_MEMCG_AWARE) { > + err = prealloc_memcg_shrinker(shrinker); > + if (err == -ENOSYS) > + shrinker->flags &= ~SHRINKER_MEMCG_AWARE; > + else if (err == 0) > + goto done; > + else > + goto err_flags; > + } > + > + /* > + * The nr_deferred is available on per memcg level for memcg aware > + * shrinkers, so only allocate nr_deferred in the following cases: > + * - non memcg aware shrinkers > + * - !CONFIG_MEMCG > + * - memcg is disabled by kernel command line > + */ > + size = sizeof(*shrinker->nr_deferred); > + if (flags & SHRINKER_NUMA_AWARE) > + size *= nr_node_ids; > + > + shrinker->nr_deferred = kzalloc(size, GFP_KERNEL); > + if (!shrinker->nr_deferred) > + goto err_flags; > + > +done: > + return shrinker; > + > +err_flags: > +#ifdef CONFIG_SHRINKER_DEBUG > + kfree_const(shrinker->name); > + shrinker->name = NULL; This could be shrinker_debugfs_name_free() > +err_name: > +#endif > + kfree(shrinker); > + return NULL; > +} > +EXPORT_SYMBOL(shrinker_alloc); > + > +void shrinker_free_non_registered(struct shrinker *shrinker) > +{ > +#ifdef CONFIG_SHRINKER_DEBUG > + kfree_const(shrinker->name); > + shrinker->name = NULL; This could be shrinker_debugfs_name_free() > +#endif > + if (shrinker->flags & SHRINKER_MEMCG_AWARE) { > + down_write(&shrinker_rwsem); > + unregister_memcg_shrinker(shrinker); > + up_write(&shrinker_rwsem); > + } > + > + kfree(shrinker->nr_deferred); > + shrinker->nr_deferred = NULL; > + > + kfree(shrinker); > +} > +EXPORT_SYMBOL(shrinker_free_non_registered); > + > +void shrinker_register(struct shrinker *shrinker) > +{ > + down_write(&shrinker_rwsem); > + list_add_tail(&shrinker->list, &shrinker_list); > + shrinker->flags |= SHRINKER_REGISTERED; > + shrinker_debugfs_add(shrinker); > + up_write(&shrinker_rwsem); > +} > +EXPORT_SYMBOL(shrinker_register); > + > +void shrinker_unregister(struct shrinker *shrinker) You have made all shrinkers to be dynamically allocated, so we should prevent users from allocating shrinkers statically and use this function to unregister it. It is better to add a flag like SHRINKER_ALLOCATED which is set in shrinker_alloc(), and check whether it is set in shrinker_unregister(), if not maybe a warning should be added to tell the users what happened. > +{ > + struct dentry *debugfs_entry; > + int debugfs_id; > + > + if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED)) > + return; > + > + down_write(&shrinker_rwsem); > + list_del(&shrinker->list); > + shrinker->flags &= ~SHRINKER_REGISTERED; > + if (shrinker->flags & SHRINKER_MEMCG_AWARE) > + unregister_memcg_shrinker(shrinker); > + debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); In the internal of this function, you also could use shrinker_debugfs_name_free(). Thanks. > + up_write(&shrinker_rwsem); > + > + shrinker_debugfs_remove(debugfs_entry, debugfs_id); > + > + kfree(shrinker->nr_deferred); > + shrinker->nr_deferred = NULL; > + > + kfree(shrinker); > +} > +EXPORT_SYMBOL(shrinker_unregister); > + > /* > * Add a shrinker callback to be called from the vm. > */
Hi Muchun, On 2023/7/25 17:02, Muchun Song wrote: > > > On 2023/7/24 17:43, Qi Zheng wrote: >> 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_free_non_registered() >> >> Used to destroy the non-registered shrinker instance. > > At least I don't like this name. I know you want to tell others > this function only should be called when shrinker has not been > registed but allocated. Maybe shrinker_free() is more simple. > And and a comment to tell the users when to use it. OK, if no one else objects, I will change it to shrinker_free() in the next version. > >> >> 3. shrinker_register() >> >> Used to register the shrinker instance, which is same as the current >> register_shrinker_prepared(). >> >> 4. shrinker_unregister() >> >> Used to unregister 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 uncoverted shrinkers in the new >> setup. >> ``` >> >> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> >> --- >> include/linux/shrinker.h | 6 +++ >> mm/shrinker.c | 113 +++++++++++++++++++++++++++++++++++++++ >> 2 files changed, 119 insertions(+) >> >> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h >> index 961cb84e51f5..296f5e163861 100644 >> --- a/include/linux/shrinker.h >> +++ b/include/linux/shrinker.h >> @@ -70,6 +70,8 @@ struct shrinker { >> int seeks; /* seeks to recreate an obj */ >> unsigned flags; >> + void *private_data; >> + >> /* These are for internal use */ >> struct list_head list; >> #ifdef CONFIG_MEMCG >> @@ -98,6 +100,10 @@ struct shrinker { >> unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup >> *memcg, >> int priority); >> +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, >> ...); >> +void shrinker_free_non_registered(struct shrinker *shrinker); >> +void shrinker_register(struct shrinker *shrinker); >> +void shrinker_unregister(struct shrinker *shrinker); >> extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker, >> const char *fmt, ...); >> diff --git a/mm/shrinker.c b/mm/shrinker.c >> index 0a32ef42f2a7..d820e4cc5806 100644 >> --- a/mm/shrinker.c >> +++ b/mm/shrinker.c >> @@ -548,6 +548,119 @@ unsigned long shrink_slab(gfp_t gfp_mask, int >> nid, struct mem_cgroup *memcg, >> return freed; >> } >> +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, >> ...) >> +{ >> + struct shrinker *shrinker; >> + unsigned int size; >> + va_list __maybe_unused ap; >> + int err; >> + >> + shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL); >> + if (!shrinker) >> + return NULL; >> + >> +#ifdef CONFIG_SHRINKER_DEBUG >> + va_start(ap, fmt); >> + shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap); >> + va_end(ap); >> + if (!shrinker->name) >> + goto err_name; >> +#endif > > So why not introduce another helper to handle this and declare it > as a void function when !CONFIG_SHRINKER_DEBUG? Something like the > following: > > #ifdef CONFIG_SHRINKER_DEBUG > static int shrinker_debugfs_name_alloc(struct shrinker *shrinker, const > char *fmt, > va_list vargs) > > { > shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, vargs); > return shrinker->name ? 0 : -ENOMEM; > } > #else > static int shrinker_debugfs_name_alloc(struct shrinker *shrinker, const > char *fmt, > va_list vargs) > { > return 0; > } > #endif Will do in the next version. > >> + shrinker->flags = flags; >> + >> + if (flags & SHRINKER_MEMCG_AWARE) { >> + err = prealloc_memcg_shrinker(shrinker); >> + if (err == -ENOSYS) >> + shrinker->flags &= ~SHRINKER_MEMCG_AWARE; >> + else if (err == 0) >> + goto done; >> + else >> + goto err_flags; >> + } >> + >> + /* >> + * The nr_deferred is available on per memcg level for memcg aware >> + * shrinkers, so only allocate nr_deferred in the following cases: >> + * - non memcg aware shrinkers >> + * - !CONFIG_MEMCG >> + * - memcg is disabled by kernel command line >> + */ >> + size = sizeof(*shrinker->nr_deferred); >> + if (flags & SHRINKER_NUMA_AWARE) >> + size *= nr_node_ids; >> + >> + shrinker->nr_deferred = kzalloc(size, GFP_KERNEL); >> + if (!shrinker->nr_deferred) >> + goto err_flags; >> + >> +done: >> + return shrinker; >> + >> +err_flags: >> +#ifdef CONFIG_SHRINKER_DEBUG >> + kfree_const(shrinker->name); >> + shrinker->name = NULL; > > This could be shrinker_debugfs_name_free() Will do. > >> +err_name: >> +#endif >> + kfree(shrinker); >> + return NULL; >> +} >> +EXPORT_SYMBOL(shrinker_alloc); >> + >> +void shrinker_free_non_registered(struct shrinker *shrinker) >> +{ >> +#ifdef CONFIG_SHRINKER_DEBUG >> + kfree_const(shrinker->name); >> + shrinker->name = NULL; > > This could be shrinker_debugfs_name_free() > >> +#endif >> + if (shrinker->flags & SHRINKER_MEMCG_AWARE) { >> + down_write(&shrinker_rwsem); >> + unregister_memcg_shrinker(shrinker); >> + up_write(&shrinker_rwsem); >> + } >> + >> + kfree(shrinker->nr_deferred); >> + shrinker->nr_deferred = NULL; >> + >> + kfree(shrinker); >> +} >> +EXPORT_SYMBOL(shrinker_free_non_registered); >> + >> +void shrinker_register(struct shrinker *shrinker) >> +{ >> + down_write(&shrinker_rwsem); >> + list_add_tail(&shrinker->list, &shrinker_list); >> + shrinker->flags |= SHRINKER_REGISTERED; >> + shrinker_debugfs_add(shrinker); >> + up_write(&shrinker_rwsem); >> +} >> +EXPORT_SYMBOL(shrinker_register); >> + >> +void shrinker_unregister(struct shrinker *shrinker) > > You have made all shrinkers to be dynamically allocated, so > we should prevent users from allocating shrinkers statically and > use this function to unregister it. It is better to add a > flag like SHRINKER_ALLOCATED which is set in shrinker_alloc(), > and check whether it is set in shrinker_unregister(), if not > maybe a warning should be added to tell the users what happened. Make sense, will do. > >> +{ >> + struct dentry *debugfs_entry; >> + int debugfs_id; >> + >> + if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED)) >> + return; >> + >> + down_write(&shrinker_rwsem); >> + list_del(&shrinker->list); >> + shrinker->flags &= ~SHRINKER_REGISTERED; >> + if (shrinker->flags & SHRINKER_MEMCG_AWARE) >> + unregister_memcg_shrinker(shrinker); >> + debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); > > In the internal of this function, you also could use > shrinker_debugfs_name_free(). Yeah, will do. Thanks, Qi > > Thanks. > >> + up_write(&shrinker_rwsem); >> + >> + shrinker_debugfs_remove(debugfs_entry, debugfs_id); >> + >> + kfree(shrinker->nr_deferred); >> + shrinker->nr_deferred = NULL; >> + >> + kfree(shrinker); >> +} >> +EXPORT_SYMBOL(shrinker_unregister); >> + >> /* >> * Add a shrinker callback to be called from the vm. >> */ >
On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote: > 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_free_non_registered() > > Used to destroy the non-registered shrinker instance. This is a bit nasty > > 3. shrinker_register() > > Used to register the shrinker instance, which is same as the current > register_shrinker_prepared(). > > 4. shrinker_unregister() rename this "shrinker_free()" and key the two different freeing cases on the SHRINKER_REGISTERED bit rather than mostly duplicating the two. void shrinker_free(struct shrinker *shrinker) { struct dentry *debugfs_entry = NULL; int debugfs_id; if (!shrinker) return; down_write(&shrinker_rwsem); if (shrinker->flags & SHRINKER_REGISTERED) { list_del(&shrinker->list); debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); } else if (IS_ENABLED(CONFIG_SHRINKER_DEBUG)) { kfree_const(shrinker->name); } if (shrinker->flags & SHRINKER_MEMCG_AWARE) unregister_memcg_shrinker(shrinker); up_write(&shrinker_rwsem); if (debugfs_entry) shrinker_debugfs_remove(debugfs_entry, debugfs_id); kfree(shrinker->nr_deferred); kfree(shrinker); } EXPORT_SYMBOL_GPL(shrinker_free);
Hi Dave, On 2023/7/26 15:26, Dave Chinner wrote: > On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote: >> 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_free_non_registered() >> >> Used to destroy the non-registered shrinker instance. > > This is a bit nasty > >> >> 3. shrinker_register() >> >> Used to register the shrinker instance, which is same as the current >> register_shrinker_prepared(). >> >> 4. shrinker_unregister() > > rename this "shrinker_free()" and key the two different freeing > cases on the SHRINKER_REGISTERED bit rather than mostly duplicating > the two. OK, will do in the next version. > > void shrinker_free(struct shrinker *shrinker) > { > struct dentry *debugfs_entry = NULL; > int debugfs_id; > > if (!shrinker) > return; > > down_write(&shrinker_rwsem); > if (shrinker->flags & SHRINKER_REGISTERED) { > list_del(&shrinker->list); > debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); > } else if (IS_ENABLED(CONFIG_SHRINKER_DEBUG)) { > kfree_const(shrinker->name); > } > > if (shrinker->flags & SHRINKER_MEMCG_AWARE) > unregister_memcg_shrinker(shrinker); > up_write(&shrinker_rwsem); > > if (debugfs_entry) > shrinker_debugfs_remove(debugfs_entry, debugfs_id); > > kfree(shrinker->nr_deferred); > kfree(shrinker); > } > EXPORT_SYMBOL_GPL(shrinker_free); Ah, I will change all new APIs to use EXPORT_SYMBOL_GPL(). Thanks, Qi >
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h index 961cb84e51f5..296f5e163861 100644 --- a/include/linux/shrinker.h +++ b/include/linux/shrinker.h @@ -70,6 +70,8 @@ struct shrinker { int seeks; /* seeks to recreate an obj */ unsigned flags; + void *private_data; + /* These are for internal use */ struct list_head list; #ifdef CONFIG_MEMCG @@ -98,6 +100,10 @@ struct shrinker { unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg, int priority); +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...); +void shrinker_free_non_registered(struct shrinker *shrinker); +void shrinker_register(struct shrinker *shrinker); +void shrinker_unregister(struct shrinker *shrinker); extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...); diff --git a/mm/shrinker.c b/mm/shrinker.c index 0a32ef42f2a7..d820e4cc5806 100644 --- a/mm/shrinker.c +++ b/mm/shrinker.c @@ -548,6 +548,119 @@ unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg, return freed; } +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...) +{ + struct shrinker *shrinker; + unsigned int size; + va_list __maybe_unused ap; + int err; + + shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL); + if (!shrinker) + return NULL; + +#ifdef CONFIG_SHRINKER_DEBUG + va_start(ap, fmt); + shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap); + va_end(ap); + if (!shrinker->name) + goto err_name; +#endif + shrinker->flags = flags; + + if (flags & SHRINKER_MEMCG_AWARE) { + err = prealloc_memcg_shrinker(shrinker); + if (err == -ENOSYS) + shrinker->flags &= ~SHRINKER_MEMCG_AWARE; + else if (err == 0) + goto done; + else + goto err_flags; + } + + /* + * The nr_deferred is available on per memcg level for memcg aware + * shrinkers, so only allocate nr_deferred in the following cases: + * - non memcg aware shrinkers + * - !CONFIG_MEMCG + * - memcg is disabled by kernel command line + */ + size = sizeof(*shrinker->nr_deferred); + if (flags & SHRINKER_NUMA_AWARE) + size *= nr_node_ids; + + shrinker->nr_deferred = kzalloc(size, GFP_KERNEL); + if (!shrinker->nr_deferred) + goto err_flags; + +done: + return shrinker; + +err_flags: +#ifdef CONFIG_SHRINKER_DEBUG + kfree_const(shrinker->name); + shrinker->name = NULL; +err_name: +#endif + kfree(shrinker); + return NULL; +} +EXPORT_SYMBOL(shrinker_alloc); + +void shrinker_free_non_registered(struct shrinker *shrinker) +{ +#ifdef CONFIG_SHRINKER_DEBUG + kfree_const(shrinker->name); + shrinker->name = NULL; +#endif + if (shrinker->flags & SHRINKER_MEMCG_AWARE) { + down_write(&shrinker_rwsem); + unregister_memcg_shrinker(shrinker); + up_write(&shrinker_rwsem); + } + + kfree(shrinker->nr_deferred); + shrinker->nr_deferred = NULL; + + kfree(shrinker); +} +EXPORT_SYMBOL(shrinker_free_non_registered); + +void shrinker_register(struct shrinker *shrinker) +{ + down_write(&shrinker_rwsem); + list_add_tail(&shrinker->list, &shrinker_list); + shrinker->flags |= SHRINKER_REGISTERED; + shrinker_debugfs_add(shrinker); + up_write(&shrinker_rwsem); +} +EXPORT_SYMBOL(shrinker_register); + +void shrinker_unregister(struct shrinker *shrinker) +{ + struct dentry *debugfs_entry; + int debugfs_id; + + if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED)) + return; + + down_write(&shrinker_rwsem); + list_del(&shrinker->list); + shrinker->flags &= ~SHRINKER_REGISTERED; + if (shrinker->flags & SHRINKER_MEMCG_AWARE) + unregister_memcg_shrinker(shrinker); + debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); + up_write(&shrinker_rwsem); + + shrinker_debugfs_remove(debugfs_entry, debugfs_id); + + kfree(shrinker->nr_deferred); + shrinker->nr_deferred = NULL; + + kfree(shrinker); +} +EXPORT_SYMBOL(shrinker_unregister); + /* * Add a shrinker callback to be called from the vm. */
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_free_non_registered() Used to destroy the non-registered shrinker instance. 3. shrinker_register() Used to register the shrinker instance, which is same as the current register_shrinker_prepared(). 4. shrinker_unregister() Used to unregister 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 uncoverted shrinkers in the new setup. ``` Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> --- include/linux/shrinker.h | 6 +++ mm/shrinker.c | 113 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 119 insertions(+)