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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1725480632; bh=BCTC0j7Sgt78nAVhjEBahOu6sqSOJXuTGyThZOs7DMw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=N1ZUYDki6pQzsFJbVYZ2mvnup9ye+l8CjwIpVH8rYWehMJ0ToPGg1fwvOA7xJydMl wigBPsYCdZ7vdai7typmbwIY4M2yM2NCSl6sRltUPgKei26qhLJs/2AHVgXEwLmJ82 VZ7JOxn3jDWpq6cpRD9UUwMQHDwTLCMW36T2IVdseCvZayslrIfcyI+VYtH86RJDZX Ikk392l2VhWYGA1asgKjwpM+oXYYgwdAKYpkQdNcaTdVjVKhtCn36KU4+WfMR+YQX6 uQDLJMoOfA01tLwXWYZFcZ2zy6WBx8UW5ztyCToO15wAQ/lK2kbrPIwRtPPQp9llts SNiiKVDbVg5CA== Date: Wed, 4 Sep 2024 22:10:27 +0200 From: Christian Brauner To: Linus Torvalds Cc: Vlastimil Babka , Mike Rapoport , Jens Axboe , Jann Horn , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v2 02/15] slab: add struct kmem_cache_args Message-ID: <20240904-kopfarbeit-zugbegleiter-c8f5dea4f6a5@brauner> References: <20240903-work-kmem_cache_args-v2-0-76f97e9a4560@kernel.org> <20240903-work-kmem_cache_args-v2-2-76f97e9a4560@kernel.org> <9303896a-e3c8-4dc3-926b-c7e8fc75cf6b@suse.cz> <3ade6827-701d-4b50-b9bd-96c60ba38658@suse.cz> <20240904-kauffreudig-bauch-c2890b265e7e@brauner> MIME-Version: 1.0 Content-Type: multipart/mixed; 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charset=utf-8 Content-Disposition: inline On Wed, Sep 04, 2024 at 11:53:05AM GMT, Linus Torvalds wrote: > On Wed, 4 Sept 2024 at 11:21, Christian Brauner wrote: > > > > Sure. So can you fold your suggestion above and the small diff below > > into the translation layer patch? > > Please don't. > > This seems horrible. First you have a _Generic() macro that turns NULL > into the same function that a proper __kmem_cache_create_args() with a > real argument uses, and then you make that function check for NULL and > turn it into something else. > > That seems *entirely* pointless. > > I think the right model is to either > > (a) not allow a NULL pointer at all (ie not have a _Generic() case > for 'void *') and just error for that behavior Fine by me and what this did originally by erroring out with a compile time error. > > OR > > (b) make a NULL pointer explicitly go to some other function than the > one that gets a proper pointer > > but not this "do extra work in the function to make it accept the NULL > we shunted to it". > > IOW, something like this: > > #define kmem_cache_create(__name, __object_size, __args, ...) \ > _Generic((__args), \ > struct kmem_cache_args *: __kmem_cache_create_args, \ > void *: __kmem_cache_default_args, \ > default: __kmem_cache_create)(__name, __object_size, > __args, __VA_ARGS__) > > and then we have > > static inline struct kmem_cache *__kmem_cache_default_args(const char *name, > unsigned int object_size, > struct kmem_cache_args *args, > slab_flags_t flags) > { WARN_ON_ONCE(args); // It had *better* be NULL, not some random 'void *' > return __kmem_cache_create_args(name, size, &kmem_args, flags); } > > which basically just does a "turn NULL into &kmem_args" thing. > > Notice how that does *not* add some odd NULL pointer check to the main > path (and the WARN_ON_ONCE() check should be compiled away for any > actual constant NULL argument, which is the only valid reason to have > that 'void *' anyway). Also fine by me. See appended updated patch. --dnhoovy3cfeicfu5 Content-Type: text/x-diff; charset=utf-8 Content-Disposition: attachment; filename="0001-slab-create-kmem_cache_create-compatibility-layer.patch" >From ede72f93668827497fb8d1c0f7286cfb4bd4f204 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Tue, 3 Sep 2024 14:49:49 +0200 Subject: [PATCH] slab: create kmem_cache_create() compatibility layer Use _Generic() to create a compatibility layer that type switches on the third argument to either call __kmem_cache_create() or __kmem_cache_create_args(). If NULL is passed for the struct kmem_cache_args argument use default args making porting for callers that don't care about additional arguments easy. Signed-off-by: Christian Brauner --- include/linux/slab.h | 29 ++++++++++++++++++++++++++--- mm/slab_common.c | 10 +++++----- 2 files changed, 31 insertions(+), 8 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index aced16a08700..d406d00cabbb 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -261,9 +261,10 @@ struct kmem_cache *__kmem_cache_create_args(const char *name, unsigned int object_size, struct kmem_cache_args *args, slab_flags_t flags); -struct kmem_cache *kmem_cache_create(const char *name, unsigned int size, - unsigned int align, slab_flags_t flags, - void (*ctor)(void *)); + +struct kmem_cache *__kmem_cache_create(const char *name, unsigned int size, + unsigned int align, slab_flags_t flags, + void (*ctor)(void *)); struct kmem_cache *kmem_cache_create_usercopy(const char *name, unsigned int size, unsigned int align, slab_flags_t flags, @@ -272,6 +273,28 @@ struct kmem_cache *kmem_cache_create_usercopy(const char *name, struct kmem_cache *kmem_cache_create_rcu(const char *name, unsigned int size, unsigned int freeptr_offset, slab_flags_t flags); + +/* If NULL is passed for @args, use this variant with default arguments. */ +static inline struct kmem_cache * +__kmem_cache_default_args(const char *name, unsigned int size, + const struct kmem_cache_args *args, + slab_flags_t flags) +{ + struct kmem_cache_args kmem_default_args = {}; + + /* Make sure we don't get passed garbage. */ + if (WARN_ON_ONCE(args)) + return NULL; + + return __kmem_cache_create_args(name, size, &kmem_default_args, flags); +} + +#define kmem_cache_create(__name, __object_size, __args, ...) \ + _Generic((__args), \ + struct kmem_cache_args *: __kmem_cache_create_args, \ + void *: __kmem_cache_default_args, \ + default: __kmem_cache_create)(__name, __object_size, __args, __VA_ARGS__) + void kmem_cache_destroy(struct kmem_cache *s); int kmem_cache_shrink(struct kmem_cache *s); diff --git a/mm/slab_common.c b/mm/slab_common.c index 19ae3dd6e36f..418459927670 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -383,7 +383,7 @@ kmem_cache_create_usercopy(const char *name, unsigned int size, EXPORT_SYMBOL(kmem_cache_create_usercopy); /** - * kmem_cache_create - Create a cache. + * __kmem_cache_create - Create a cache. * @name: A string which is used in /proc/slabinfo to identify this cache. * @size: The size of objects to be created in this cache. * @align: The required alignment for the objects. @@ -407,9 +407,9 @@ EXPORT_SYMBOL(kmem_cache_create_usercopy); * * Return: a pointer to the cache on success, NULL on failure. */ -struct kmem_cache * -kmem_cache_create(const char *name, unsigned int size, unsigned int align, - slab_flags_t flags, void (*ctor)(void *)) +struct kmem_cache *__kmem_cache_create(const char *name, unsigned int size, + unsigned int align, slab_flags_t flags, + void (*ctor)(void *)) { struct kmem_cache_args kmem_args = { .align = align, @@ -418,7 +418,7 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align, return __kmem_cache_create_args(name, size, &kmem_args, flags); } -EXPORT_SYMBOL(kmem_cache_create); +EXPORT_SYMBOL(__kmem_cache_create); /** * kmem_cache_create_rcu - Create a SLAB_TYPESAFE_BY_RCU cache. -- 2.45.2 --dnhoovy3cfeicfu5--