Messages in this thread Patch in this message | | | Date | Mon, 18 Sep 2023 17:03:31 +0800 | Subject | Re: [PATCH v6 01/45] mm: shrinker: add infrastructure for dynamically allocating shrinker | From | Muchun Song <> |
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On 2023/9/11 17:44, 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_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. > ``` > > Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> > --- > include/linux/shrinker.h | 7 +++ > mm/internal.h | 11 +++++ > mm/shrinker.c | 102 +++++++++++++++++++++++++++++++++++++++ > mm/shrinker_debug.c | 17 ++++++- > 4 files changed, 135 insertions(+), 2 deletions(-) > > diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h > index 6b5843c3b827..3f3fd9974ce5 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 > @@ -95,6 +97,11 @@ struct shrinker { > * non-MEMCG_AWARE shrinker should not have this flag set. > */ > #define SHRINKER_NONSLAB (1 << 3) > +#define SHRINKER_ALLOCATED (1 << 4)
It is better to add a comment here to tell users it is only used by internals of shrinker. The users are not supposed to pass this flag to shrink APIs.
> + > +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...); > +void shrinker_register(struct shrinker *shrinker); > +void shrinker_free(struct shrinker *shrinker); > > extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker, > const char *fmt, ...); > diff --git a/mm/internal.h b/mm/internal.h > index 0471d6326d01..5587cae20ebf 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -1161,6 +1161,9 @@ unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg, > > #ifdef CONFIG_SHRINKER_DEBUG > extern int shrinker_debugfs_add(struct shrinker *shrinker); > +extern int shrinker_debugfs_name_alloc(struct shrinker *shrinker, > + const char *fmt, va_list ap); > +extern void shrinker_debugfs_name_free(struct shrinker *shrinker); > extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker, > int *debugfs_id); > extern void shrinker_debugfs_remove(struct dentry *debugfs_entry, > @@ -1170,6 +1173,14 @@ static inline int shrinker_debugfs_add(struct shrinker *shrinker) > { > return 0; > } > +static inline int shrinker_debugfs_name_alloc(struct shrinker *shrinker, > + const char *fmt, va_list ap) > +{ > + return 0; > +} > +static inline void shrinker_debugfs_name_free(struct shrinker *shrinker) > +{ > +} > static inline struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker, > int *debugfs_id) > { > diff --git a/mm/shrinker.c b/mm/shrinker.c > index a16cd448b924..201211a67827 100644 > --- a/mm/shrinker.c > +++ b/mm/shrinker.c > @@ -550,6 +550,108 @@ 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 ap; > + int err; > + > + shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL); > + if (!shrinker) > + return NULL; > + > + va_start(ap, fmt); > + err = shrinker_debugfs_name_alloc(shrinker, fmt, ap); > + va_end(ap); > + if (err) > + goto err_name; > + > + shrinker->flags = flags | SHRINKER_ALLOCATED; > + shrinker->seeks = DEFAULT_SEEKS; > + > + 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;
Actually, the code here is a little confusing me when I fist look at it. I think there could be some improvements here. Something like:
if (flags & SHRINKER_MEMCG_AWARE) { err = prealloc_memcg_shrinker(shrinker); if (err == -ENOSYS) { /* Memcg is not supported and fallback to non-memcg-aware shrinker. */ shrinker->flags &= ~SHRINKER_MEMCG_AWARE; goto non-memcg; }
if (err) goto err_flags; return shrinker; }
non-memcg: [...] return shrinker;
In this case, the code becomes more clear (at least for me). We have split the code into two part, one is handling memcg-aware case, another is non-memcg-aware case. Any side will have a explicit "return" keyword to return once succeeds. It is a little implicit that the previous one uses "goto done".
And the tag of "non-memcg" is also a good annotation to tell us the following code handles non-memcg-aware case.
> + } > + > + /* > + * 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: > + shrinker_debugfs_name_free(shrinker); > +err_name: > + kfree(shrinker); > + return NULL; > +} > +EXPORT_SYMBOL_GPL(shrinker_alloc); > + > +void shrinker_register(struct shrinker *shrinker) > +{ > + if (unlikely(!(shrinker->flags & SHRINKER_ALLOCATED))) { > + pr_warn("Must use shrinker_alloc() to dynamically allocate the shrinker"); > + return; > + } > + > + 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_GPL(shrinker_register); > + > +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); > + shrinker->flags &= ~SHRINKER_REGISTERED; > + } else { > + shrinker_debugfs_name_free(shrinker);
We could remove shrinker_debugfs_name_free() calling from shrinker_debugfs_detach(), then we could call shrinker_debugfs_name_free() anyway, otherwise, it it a little weird for me. And the srinker name is allocated from shrinker_alloc(), so I think it it reasonable for shrinker_free() to free the shrinker name.
Thanks.
> + } > + > + 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); > + shrinker->nr_deferred = NULL; > + > + kfree(shrinker); > +} > +EXPORT_SYMBOL_GPL(shrinker_free); > + > /* > * Add a shrinker callback to be called from the vm. > */ > diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c > index e4ce509f619e..38452f539f40 100644 > --- a/mm/shrinker_debug.c > +++ b/mm/shrinker_debug.c > @@ -193,6 +193,20 @@ int shrinker_debugfs_add(struct shrinker *shrinker) > return 0; > } > > +int shrinker_debugfs_name_alloc(struct shrinker *shrinker, const char *fmt, > + va_list ap) > +{ > + shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap); > + > + return shrinker->name ? 0 : -ENOMEM; > +} > + > +void shrinker_debugfs_name_free(struct shrinker *shrinker) > +{ > + kfree_const(shrinker->name); > + shrinker->name = NULL; > +}
It it better to move both helpers to internal.h and mark them as inline since both are very simple enough.
Thanks.
> + > int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...) > { > struct dentry *entry; > @@ -241,8 +255,7 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker, > > lockdep_assert_held(&shrinker_rwsem); > > - kfree_const(shrinker->name); > - shrinker->name = NULL; > + shrinker_debugfs_name_free(shrinker); > > *debugfs_id = entry ? shrinker->debugfs_id : -1; > shrinker->debugfs_entry = NULL;
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