Messages in this thread | | | Date | Tue, 25 Jul 2023 17:02:47 +0800 | Subject | Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker | From | Muchun Song <> |
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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. > */
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