Re: [PATCH v6 01/45] mm: shrinker: add infrastructure for dynamically allocating shrinker

Qi Zheng
2023-09-18T12:09:04Z

On 2023/9/18 17:03, Muchun Song wrote:
>
>

...

>> @@ -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.

OK, will annotate SHRINKER_REGISTERED and SHRINKER_ALLOCATED
as flags used internally.

>
>> +
>> +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.

Make sense, will do.

>
>> +    }
>> +
>> +    /*
>> +     * 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.

OK, will do.

>
> 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.

OK, will do.

Hi Andrew, below is the cleanup patch, which has a small conflict
with [PATCH v6 41/45]:

From 5bc2b77484f5cd4616e510158f91c8877bd033ad Mon Sep 17 00:00:00 2001
From: Qi Zheng <zhengqi.arch@bytedance.com>
Date: Mon, 18 Sep 2023 10:41:15 +0000
Subject: [PATCH] mm: shrinker: some cleanup

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
include/linux/shrinker.h | 14 ++++++++------
mm/internal.h | 17 ++++++++++++++---
mm/shrinker.c | 20 ++++++++++++--------
mm/shrinker_debug.c | 16 ----------------
4 files changed, 34 insertions(+), 33 deletions(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 3f3fd9974ce5..f4a5249f00b2 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -88,16 +88,18 @@ struct shrinker {
};
#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */

-/* Flags */
-#define SHRINKER_REGISTERED (1 << 0)
-#define SHRINKER_NUMA_AWARE (1 << 1)
-#define SHRINKER_MEMCG_AWARE (1 << 2)
+/* Internal flags */
+#define SHRINKER_REGISTERED BIT(0)
+#define SHRINKER_ALLOCATED BIT(1)
+
+/* Flags for users to use */
+#define SHRINKER_NUMA_AWARE BIT(2)
+#define SHRINKER_MEMCG_AWARE BIT(3)
/*
* It just makes sense when the shrinker is also MEMCG_AWARE for now,
* non-MEMCG_AWARE shrinker should not have this flag set.
*/
-#define SHRINKER_NONSLAB (1 << 3)
-#define SHRINKER_ALLOCATED (1 << 4)
+#define SHRINKER_NONSLAB BIT(4)

struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...);
void shrinker_register(struct shrinker *shrinker);
diff --git a/mm/internal.h b/mm/internal.h
index b9a116dce28e..0f418a11c7a8 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1161,10 +1161,21 @@ unsigned long shrink_slab(gfp_t gfp_mask, int
nid, struct mem_cgroup *memcg,
int priority);

#ifdef CONFIG_SHRINKER_DEBUG
+static inline 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;
+}
+
+static inline void shrinker_debugfs_name_free(struct shrinker *shrinker)
+{
+ kfree_const(shrinker->name);
+ shrinker->name = NULL;
+}
+
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,
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 201211a67827..d1032a4d5684 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -572,18 +572,23 @@ struct shrinker *shrinker_alloc(unsigned int
flags, const char *fmt, ...)

if (flags & SHRINKER_MEMCG_AWARE) {
err = prealloc_memcg_shrinker(shrinker);
- if (err == -ENOSYS)
+ if (err == -ENOSYS) {
+ /* Memcg is not supported, fallback to non-memcg-aware shrinker. */
shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
- else if (err == 0)
- goto done;
- else
+ goto non_memcg;
+ }
+
+ if (err)
goto err_flags;
+
+ return shrinker;
}

+non_memcg:
/*
* 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
+ * - non-memcg-aware shrinkers
* - !CONFIG_MEMCG
* - memcg is disabled by kernel command line
*/
@@ -595,7 +600,6 @@ struct shrinker *shrinker_alloc(unsigned int flags,
const char *fmt, ...)
if (!shrinker->nr_deferred)
goto err_flags;

-done:
return shrinker;

err_flags:
@@ -634,10 +638,10 @@ void shrinker_free(struct shrinker *shrinker)
list_del(&shrinker->list);
debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
shrinker->flags &= ~SHRINKER_REGISTERED;
- } else {
- shrinker_debugfs_name_free(shrinker);
}

+ shrinker_debugfs_name_free(shrinker);
+
if (shrinker->flags & SHRINKER_MEMCG_AWARE)
unregister_memcg_shrinker(shrinker);
up_write(&shrinker_rwsem);
diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index 38452f539f40..24aebe7c24cc 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -193,20 +193,6 @@ 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;
-}
-
int shrinker_debugfs_rename(struct shrinker *shrinker, const char
*fmt, ...)
{
struct dentry *entry;
@@ -255,8 +241,6 @@ struct dentry *shrinker_debugfs_detach(struct
shrinker *shrinker,

lockdep_assert_held(&shrinker_rwsem);

- shrinker_debugfs_name_free(shrinker);
-
*debugfs_id = entry ? shrinker->debugfs_id : -1;
shrinker->debugfs_entry = NULL;

--
2.30.2

>
> 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;
>