[PATCH] mm: Fixed incorrect comment for _kmem_cache_create function

[PATCH] mm: Fixed incorrect comment for _kmem_cache_create function

[zhaoxinchao]

From: zhaoxinchao <chrisxinchao@outlook.com>

Actually __kmem_cache_create() returns a status :
0 is success
others are failed.

Signed-off-by: zhaoxinchao <chrisxinchao@outlook.com>
---
 mm/slab.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab.c b/mm/slab.c
index ca4822f6b..65985f767 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1901,7 +1901,7 @@ static bool set_on_slab_cache(struct kmem_cache *cachep,
  * @cachep: cache management descriptor
  * @flags: SLAB flags
  *
- * Returns a ptr to the cache on success, NULL on failure.
+ * Returns zero on success, others on failure.
  * Cannot be called within a int, but can be interrupted.
  * The @ctor is run when new pages are allocated by the cache.
  *
-- 
2.39.2

Re: [PATCH] mm: Fixed incorrect comment for _kmem_cache_create function

[Bagas Sanjaya]

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On Mon, Apr 10, 2023 at 05:01:42PM +0800, zhaoxinchao wrote:
> - * Returns a ptr to the cache on success, NULL on failure.
> + * Returns zero on success, others on failure.

Can you explain what these other return values are? I have skimmed on
__kmem_cache_create() kerneldoc and the function returns error in that
case.

-- 
An old man doll... just what I always wanted! - Clara

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[PATCH v2] mm: Fixed incorrect comment for _kmem_cache_create function

[zhaoxinchao]

From: zhaoxinchao <chrisxinchao@outlook.com>

Actually __kmem_cache_create() returns a status :
0 is success
nonezero are failed.

This function has three return positions. In addition to successfully
return 0, the first failed position will return - E2BIG, and the second
position will return nonzero value for setup_cpu_cache function failure.

Signed-off-by: zhaoxinchao <chrisxinchao@outlook.com>
---
 mm/slab.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/slab.c b/mm/slab.c
index edbe722fb..399daa4d0 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1893,7 +1893,12 @@ static bool set_on_slab_cache(struct kmem_cache *cachep,
  * @cachep: cache management descriptor
  * @flags: SLAB flags
  *
- * Returns a ptr to the cache on success, NULL on failure.
+ * Returns zero on success, nonzero on failure.
+ * This function has three return positions.
+ * In addition to successfully return 0, the
+ * first failed position will return - E2BIG,
+ * and the second position will return nonzero
+ * value for setup_cpu_cache function failure.
  * Cannot be called within an int, but can be interrupted.
  * The @ctor is run when new pages are allocated by the cache.
  *
-- 
2.39.2

Re: [PATCH v2] mm: Fixed incorrect comment for _kmem_cache_create function

[Bagas Sanjaya]

On 4/11/23 16:13, zhaoxinchao wrote:
> diff --git a/mm/slab.c b/mm/slab.c
> index edbe722fb..399daa4d0 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1893,7 +1893,12 @@ static bool set_on_slab_cache(struct kmem_cache *cachep,
>   * @cachep: cache management descriptor
>   * @flags: SLAB flags
>   *
> - * Returns a ptr to the cache on success, NULL on failure.
> + * Returns zero on success, nonzero on failure.
> + * This function has three return positions.
> + * In addition to successfully return 0, the
> + * first failed position will return - E2BIG,
> + * and the second position will return nonzero
> + * value for setup_cpu_cache function failure.
>   * Cannot be called within an int, but can be interrupted.
>   * The @ctor is run when new pages are allocated by the cache.
>   *

I don't see any visible changes in my htmldocs build (since the
kernel-doc is for inline version of kmem_cache_create()).
You will also need to update kernel-doc comment for
kmem_cache_create_usercopy() and kmem_cache_create() in
mm/slab_common.c. Since the latter function is actually a wrapper
on the former, the return value description (Return: field)
should be same on both.

Thanks.

-- 
An old man doll... just what I always wanted! - Clara

答复: [PATCH v2] mm: Fixed incorrect comment for _kmem_cache_create function

[zhao xinchao]

I don't think kmem_cache_create is associated with __kmem_cache_create, 
__kmem_cache_create is not exported as an API, it is a function called internally by the kernel.
So the kernel documentation does not document this internal interface.

-----邮件原件-----
发件人: Bagas Sanjaya [mailto:bagasdotme@gmail.com] 
发送时间: 2023年4月12日 11:40
收件人: zhaoxinchao <ChrisXinchao@outlook.com>
抄送: akpm@linux-foundation.org; cl@linux.com; iamjoonsoo.kim@lge.com; linux-kernel@vger.kernel.org; linux-mm@kvack.org; penberg@kernel.org; rientjes@google.com; vbabka@suse.cz
主题: Re: [PATCH v2] mm: Fixed incorrect comment for _kmem_cache_create function

On 4/11/23 16:13, zhaoxinchao wrote:
> diff --git a/mm/slab.c b/mm/slab.c
> index edbe722fb..399daa4d0 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1893,7 +1893,12 @@ static bool set_on_slab_cache(struct kmem_cache *cachep,
>   * @cachep: cache management descriptor
>   * @flags: SLAB flags
>   *
> - * Returns a ptr to the cache on success, NULL on failure.
> + * Returns zero on success, nonzero on failure.
> + * This function has three return positions.
> + * In addition to successfully return 0, the
> + * first failed position will return - E2BIG,
> + * and the second position will return nonzero
> + * value for setup_cpu_cache function failure.
>   * Cannot be called within an int, but can be interrupted.
>   * The @ctor is run when new pages are allocated by the cache.
>   *

I don't see any visible changes in my htmldocs build (since the kernel-doc is for inline version of kmem_cache_create()).
You will also need to update kernel-doc comment for
kmem_cache_create_usercopy() and kmem_cache_create() in mm/slab_common.c. Since the latter function is actually a wrapper on the former, the return value description (Return: field) should be same on both.

Thanks.

--
An old man doll... just what I always wanted! - Clara

Re: [PATCH v2] mm: Fixed incorrect comment for _kmem_cache_create function

[Vlastimil Babka]

On 4/11/23 11:13, zhaoxinchao wrote:
> From: zhaoxinchao <chrisxinchao@outlook.com>
> 
> Actually __kmem_cache_create() returns a status :
> 0 is success
> nonezero are failed.
> 
> This function has three return positions. In addition to successfully
> return 0, the first failed position will return - E2BIG, and the second
> position will return nonzero value for setup_cpu_cache function failure.
> 
> Signed-off-by: zhaoxinchao <chrisxinchao@outlook.com>
> ---
>  mm/slab.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index edbe722fb..399daa4d0 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1893,7 +1893,12 @@ static bool set_on_slab_cache(struct kmem_cache *cachep,
>   * @cachep: cache management descriptor
>   * @flags: SLAB flags
>   *
> - * Returns a ptr to the cache on success, NULL on failure.
> + * Returns zero on success, nonzero on failure.

OK.

> + * This function has three return positions.
> + * In addition to successfully return 0, the
> + * first failed position will return - E2BIG,
> + * and the second position will return nonzero
> + * value for setup_cpu_cache function failure.

I don't think we need to be so specific here, so we can drop this block.

>   * Cannot be called within an int, but can be interrupted.
>   * The @ctor is run when new pages are allocated by the cache.
>   *

You missed that there's also:

 * Return: a pointer to the created cache or %NULL in case of error
 */
int __kmem_cache_create(struct kmem_cache *cachep, slab_flags_t flags)

I guess we can drop the first mention of returns and fix up this one.
Also I'd make this a non-kerneldoc comment (/* instead of /**) as
it's for a SLAB-specific internal implementation only. Only
kmem_cache_create() is meant as an API.

[PATCH v3] mm: Fixed incorrect comment for _kmem_cache_create function

[zhaoxinchao]

From: zhaoxinchao <chrisxinchao@outlook.com>

Actually __kmem_cache_create() returns a status :
0 is success
nonezero are failed.

This function has three return positions. In addition to successfully
return 0, the first failed position will return - E2BIG, and the second
position will return nonzero value for setup_cpu_cache function failure.

Signed-off-by: zhaoxinchao <chrisxinchao@outlook.com>
---
 mm/slab.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index edbe722fb..ebd326f07 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1888,14 +1888,17 @@ static bool set_on_slab_cache(struct kmem_cache *cachep,
 	return true;
 }
 
-/**
+/*
  * __kmem_cache_create - Create a cache.
  * @cachep: cache management descriptor
  * @flags: SLAB flags
  *
- * Returns a ptr to the cache on success, NULL on failure.
- * Cannot be called within an int, but can be interrupted.
- * The @ctor is run when new pages are allocated by the cache.
+ * Returns zero on success, nonzero on failure.
+ * This function has three return positions.
+ * In addition to successfully return 0, the
+ * first failed position will return - E2BIG,
+ * and the second position will return nonzero
+ * value for setup_cpu_cache function failure.
  *
  * The flags are
  *
@@ -1908,8 +1911,6 @@ static bool set_on_slab_cache(struct kmem_cache *cachep,
  * %SLAB_HWCACHE_ALIGN - Align the objects in this cache to a hardware
  * cacheline.  This can be beneficial if you're counting cycles as closely
  * as davem.
- *
- * Return: a pointer to the created cache or %NULL in case of error
  */
 int __kmem_cache_create(struct kmem_cache *cachep, slab_flags_t flags)
 {
-- 
2.39.2

Re: [PATCH v3] mm: Fixed incorrect comment for _kmem_cache_create function

[Vlastimil Babka]

On 4/18/23 04:05, zhaoxinchao wrote:
> From: zhaoxinchao <chrisxinchao@outlook.com>
> 
> Actually __kmem_cache_create() returns a status :
> 0 is success
> nonezero are failed.
> 
> This function has three return positions. In addition to successfully
> return 0, the first failed position will return - E2BIG, and the second
> position will return nonzero value for setup_cpu_cache function failure.

Adjusted a bit.

> Signed-off-by: zhaoxinchao <chrisxinchao@outlook.com>
> ---
>  mm/slab.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index edbe722fb..ebd326f07 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1888,14 +1888,17 @@ static bool set_on_slab_cache(struct kmem_cache *cachep,
>  	return true;
>  }
>  
> -/**
> +/*
>   * __kmem_cache_create - Create a cache.
>   * @cachep: cache management descriptor
>   * @flags: SLAB flags
>   *
> - * Returns a ptr to the cache on success, NULL on failure.
> - * Cannot be called within an int, but can be interrupted.
> - * The @ctor is run when new pages are allocated by the cache.
> + * Returns zero on success, nonzero on failure.
> + * This function has three return positions.
> + * In addition to successfully return 0, the
> + * first failed position will return - E2BIG,
> + * and the second position will return nonzero
> + * value for setup_cpu_cache function failure.

In v2 I recommended dropping the detailed description. Removed it when
merging. The result is merged for 6.5 here:

https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git/log/?h=slab/for-6.5/trivial

Thanks!

>   *
>   * The flags are
>   *
> @@ -1908,8 +1911,6 @@ static bool set_on_slab_cache(struct kmem_cache *cachep,
>   * %SLAB_HWCACHE_ALIGN - Align the objects in this cache to a hardware
>   * cacheline.  This can be beneficial if you're counting cycles as closely
>   * as davem.
> - *
> - * Return: a pointer to the created cache or %NULL in case of error
>   */
>  int __kmem_cache_create(struct kmem_cache *cachep, slab_flags_t flags)
>  {