[PATCH] fs: hide file and bfile caches behind runtime const machinery

[PATCH] fs: hide file and bfile caches behind runtime const machinery

[Mateusz Guzik]

s/cachep/cache/ for consistency with namei and dentry caches.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---
 fs/file.c                         |  2 +-
 fs/file_table.c                   | 31 +++++++++++++++++++------------
 include/asm-generic/vmlinux.lds.h |  4 +++-
 3 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index 384c83ce768d..2c81c0b162d0 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -200,7 +200,7 @@ static struct fdtable *alloc_fdtable(unsigned int slots_wanted)
 	/*
 	 * Check if the allocation size would exceed INT_MAX. kvmalloc_array()
 	 * and kvmalloc() will warn if the allocation size is greater than
-	 * INT_MAX, as filp_cachep objects are not __GFP_NOWARN.
+	 * INT_MAX, as filp_cache objects are not __GFP_NOWARN.
 	 *
 	 * This can happen when sysctl_nr_open is set to a very high value and
 	 * a process tries to use a file descriptor near that limit. For example,
diff --git a/fs/file_table.c b/fs/file_table.c
index aaa5faaace1e..c40ec1be2899 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -30,6 +30,8 @@
 
 #include <linux/atomic.h>
 
+#include <asm/runtime-const.h>
+
 #include "internal.h"
 
 /* sysctl tunables... */
@@ -38,8 +40,10 @@ static struct files_stat_struct files_stat = {
 };
 
 /* SLAB cache for file structures */
-static struct kmem_cache *filp_cachep __ro_after_init;
-static struct kmem_cache *bfilp_cachep __ro_after_init;
+static struct kmem_cache *__filp_cache __ro_after_init;
+#define filp_cache runtime_const_ptr(__filp_cache)
+static struct kmem_cache *__bfilp_cache __ro_after_init;
+#define bfilp_cache runtime_const_ptr(__bfilp_cache)
 
 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
 
@@ -74,9 +78,9 @@ static inline void file_free(struct file *f)
 	put_cred(f->f_cred);
 	if (unlikely(f->f_mode & FMODE_BACKING)) {
 		path_put(backing_file_user_path(f));
-		kmem_cache_free(bfilp_cachep, backing_file(f));
+		kmem_cache_free(bfilp_cache, backing_file(f));
 	} else {
-		kmem_cache_free(filp_cachep, f);
+		kmem_cache_free(filp_cache, f);
 	}
 }
 
@@ -234,13 +238,13 @@ struct file *alloc_empty_file(int flags, const struct cred *cred)
 			goto over;
 	}
 
-	f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
+	f = kmem_cache_alloc(filp_cache, GFP_KERNEL);
 	if (unlikely(!f))
 		return ERR_PTR(-ENOMEM);
 
 	error = init_file(f, flags, cred);
 	if (unlikely(error)) {
-		kmem_cache_free(filp_cachep, f);
+		kmem_cache_free(filp_cache, f);
 		return ERR_PTR(error);
 	}
 
@@ -268,13 +272,13 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
 	struct file *f;
 	int error;
 
-	f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
+	f = kmem_cache_alloc(filp_cache, GFP_KERNEL);
 	if (unlikely(!f))
 		return ERR_PTR(-ENOMEM);
 
 	error = init_file(f, flags, cred);
 	if (unlikely(error)) {
-		kmem_cache_free(filp_cachep, f);
+		kmem_cache_free(filp_cache, f);
 		return ERR_PTR(error);
 	}
 
@@ -295,13 +299,13 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
 	struct backing_file *ff;
 	int error;
 
-	ff = kmem_cache_alloc(bfilp_cachep, GFP_KERNEL);
+	ff = kmem_cache_alloc(bfilp_cache, GFP_KERNEL);
 	if (unlikely(!ff))
 		return ERR_PTR(-ENOMEM);
 
 	error = init_file(&ff->file, flags, cred);
 	if (unlikely(error)) {
-		kmem_cache_free(bfilp_cachep, ff);
+		kmem_cache_free(bfilp_cache, ff);
 		return ERR_PTR(error);
 	}
 
@@ -593,14 +597,17 @@ void __init files_init(void)
 		.freeptr_offset = offsetof(struct file, f_freeptr),
 	};
 
-	filp_cachep = kmem_cache_create("filp", sizeof(struct file), &args,
+	__filp_cache = kmem_cache_create("filp", sizeof(struct file), &args,
 				SLAB_HWCACHE_ALIGN | SLAB_PANIC |
 				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
+	runtime_const_init(ptr, __filp_cache);
 
 	args.freeptr_offset = offsetof(struct backing_file, bf_freeptr);
-	bfilp_cachep = kmem_cache_create("bfilp", sizeof(struct backing_file),
+	__bfilp_cache = kmem_cache_create("bfilp", sizeof(struct backing_file),
 				&args, SLAB_HWCACHE_ALIGN | SLAB_PANIC |
 				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
+	runtime_const_init(ptr, __bfilp_cache);
+
 	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
 }
 
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 1e1580febe4b..4f8e734c4336 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -975,7 +975,9 @@
 		RUNTIME_CONST(shift, d_hash_shift)			\
 		RUNTIME_CONST(ptr, dentry_hashtable)			\
 		RUNTIME_CONST(ptr, __dentry_cache)			\
-		RUNTIME_CONST(ptr, __names_cache)
+		RUNTIME_CONST(ptr, __names_cache)			\
+		RUNTIME_CONST(ptr, __filp_cache)			\
+		RUNTIME_CONST(ptr, __bfilp_cache)
 
 /* Alignment must be consistent with (kunit_suite *) in include/kunit/test.h */
 #define KUNIT_TABLE()							\
-- 
2.48.1

Re: [PATCH] fs: hide file and bfile caches behind runtime const machinery

[Jan Kara]

On Sat 28-03-26 18:37:28, Mateusz Guzik wrote:
> s/cachep/cache/ for consistency with namei and dentry caches.
> 
> Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/file.c                         |  2 +-
>  fs/file_table.c                   | 31 +++++++++++++++++++------------
>  include/asm-generic/vmlinux.lds.h |  4 +++-
>  3 files changed, 23 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/file.c b/fs/file.c
> index 384c83ce768d..2c81c0b162d0 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -200,7 +200,7 @@ static struct fdtable *alloc_fdtable(unsigned int slots_wanted)
>  	/*
>  	 * Check if the allocation size would exceed INT_MAX. kvmalloc_array()
>  	 * and kvmalloc() will warn if the allocation size is greater than
> -	 * INT_MAX, as filp_cachep objects are not __GFP_NOWARN.
> +	 * INT_MAX, as filp_cache objects are not __GFP_NOWARN.
>  	 *
>  	 * This can happen when sysctl_nr_open is set to a very high value and
>  	 * a process tries to use a file descriptor near that limit. For example,
> diff --git a/fs/file_table.c b/fs/file_table.c
> index aaa5faaace1e..c40ec1be2899 100644
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -30,6 +30,8 @@
>  
>  #include <linux/atomic.h>
>  
> +#include <asm/runtime-const.h>
> +
>  #include "internal.h"
>  
>  /* sysctl tunables... */
> @@ -38,8 +40,10 @@ static struct files_stat_struct files_stat = {
>  };
>  
>  /* SLAB cache for file structures */
> -static struct kmem_cache *filp_cachep __ro_after_init;
> -static struct kmem_cache *bfilp_cachep __ro_after_init;
> +static struct kmem_cache *__filp_cache __ro_after_init;
> +#define filp_cache runtime_const_ptr(__filp_cache)
> +static struct kmem_cache *__bfilp_cache __ro_after_init;
> +#define bfilp_cache runtime_const_ptr(__bfilp_cache)
>  
>  static struct percpu_counter nr_files __cacheline_aligned_in_smp;
>  
> @@ -74,9 +78,9 @@ static inline void file_free(struct file *f)
>  	put_cred(f->f_cred);
>  	if (unlikely(f->f_mode & FMODE_BACKING)) {
>  		path_put(backing_file_user_path(f));
> -		kmem_cache_free(bfilp_cachep, backing_file(f));
> +		kmem_cache_free(bfilp_cache, backing_file(f));
>  	} else {
> -		kmem_cache_free(filp_cachep, f);
> +		kmem_cache_free(filp_cache, f);
>  	}
>  }
>  
> @@ -234,13 +238,13 @@ struct file *alloc_empty_file(int flags, const struct cred *cred)
>  			goto over;
>  	}
>  
> -	f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
> +	f = kmem_cache_alloc(filp_cache, GFP_KERNEL);
>  	if (unlikely(!f))
>  		return ERR_PTR(-ENOMEM);
>  
>  	error = init_file(f, flags, cred);
>  	if (unlikely(error)) {
> -		kmem_cache_free(filp_cachep, f);
> +		kmem_cache_free(filp_cache, f);
>  		return ERR_PTR(error);
>  	}
>  
> @@ -268,13 +272,13 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
>  	struct file *f;
>  	int error;
>  
> -	f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
> +	f = kmem_cache_alloc(filp_cache, GFP_KERNEL);
>  	if (unlikely(!f))
>  		return ERR_PTR(-ENOMEM);
>  
>  	error = init_file(f, flags, cred);
>  	if (unlikely(error)) {
> -		kmem_cache_free(filp_cachep, f);
> +		kmem_cache_free(filp_cache, f);
>  		return ERR_PTR(error);
>  	}
>  
> @@ -295,13 +299,13 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
>  	struct backing_file *ff;
>  	int error;
>  
> -	ff = kmem_cache_alloc(bfilp_cachep, GFP_KERNEL);
> +	ff = kmem_cache_alloc(bfilp_cache, GFP_KERNEL);
>  	if (unlikely(!ff))
>  		return ERR_PTR(-ENOMEM);
>  
>  	error = init_file(&ff->file, flags, cred);
>  	if (unlikely(error)) {
> -		kmem_cache_free(bfilp_cachep, ff);
> +		kmem_cache_free(bfilp_cache, ff);
>  		return ERR_PTR(error);
>  	}
>  
> @@ -593,14 +597,17 @@ void __init files_init(void)
>  		.freeptr_offset = offsetof(struct file, f_freeptr),
>  	};
>  
> -	filp_cachep = kmem_cache_create("filp", sizeof(struct file), &args,
> +	__filp_cache = kmem_cache_create("filp", sizeof(struct file), &args,
>  				SLAB_HWCACHE_ALIGN | SLAB_PANIC |
>  				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
> +	runtime_const_init(ptr, __filp_cache);
>  
>  	args.freeptr_offset = offsetof(struct backing_file, bf_freeptr);
> -	bfilp_cachep = kmem_cache_create("bfilp", sizeof(struct backing_file),
> +	__bfilp_cache = kmem_cache_create("bfilp", sizeof(struct backing_file),
>  				&args, SLAB_HWCACHE_ALIGN | SLAB_PANIC |
>  				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
> +	runtime_const_init(ptr, __bfilp_cache);
> +
>  	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
>  }
>  
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 1e1580febe4b..4f8e734c4336 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -975,7 +975,9 @@
>  		RUNTIME_CONST(shift, d_hash_shift)			\
>  		RUNTIME_CONST(ptr, dentry_hashtable)			\
>  		RUNTIME_CONST(ptr, __dentry_cache)			\
> -		RUNTIME_CONST(ptr, __names_cache)
> +		RUNTIME_CONST(ptr, __names_cache)			\
> +		RUNTIME_CONST(ptr, __filp_cache)			\
> +		RUNTIME_CONST(ptr, __bfilp_cache)
>  
>  /* Alignment must be consistent with (kunit_suite *) in include/kunit/test.h */
>  #define KUNIT_TABLE()							\
> -- 
> 2.48.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH] fs: hide file and bfile caches behind runtime const machinery

[Christian Brauner]

On Sat, 28 Mar 2026 18:37:28 +0100, Mateusz Guzik wrote:
> s/cachep/cache/ for consistency with namei and dentry caches.

Applied to the vfs-7.1.misc branch of the vfs/vfs.git tree.
Patches in the vfs-7.1.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-7.1.misc

[1/1] fs: hide file and bfile caches behind runtime const machinery
      https://git.kernel.org/vfs/vfs/c/1f1651d6dc2a

Re: [PATCH] fs: hide file and bfile caches behind runtime const machinery

[Al Viro]

On Sat, Mar 28, 2026 at 06:37:28PM +0100, Mateusz Guzik wrote:

> -static struct kmem_cache *filp_cachep __ro_after_init;
> -static struct kmem_cache *bfilp_cachep __ro_after_init;
> +static struct kmem_cache *__filp_cache __ro_after_init;
> +#define filp_cache runtime_const_ptr(__filp_cache)
> +static struct kmem_cache *__bfilp_cache __ro_after_init;
> +#define bfilp_cache runtime_const_ptr(__bfilp_cache)

IMO the entire runtime_const_ptr thing for caches is wrong;
statically allocated kmem_cache series got stalled, but I'm
bringing it back next cycle and this stuff is going to get
reverted as part of that.

Re: [PATCH] fs: hide file and bfile caches behind runtime const machinery

[Mateusz Guzik]

On Mon, Apr 6, 2026 at 11:13 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Sat, Mar 28, 2026 at 06:37:28PM +0100, Mateusz Guzik wrote:
>
> > -static struct kmem_cache *filp_cachep __ro_after_init;
> > -static struct kmem_cache *bfilp_cachep __ro_after_init;
> > +static struct kmem_cache *__filp_cache __ro_after_init;
> > +#define filp_cache runtime_const_ptr(__filp_cache)
> > +static struct kmem_cache *__bfilp_cache __ro_after_init;
> > +#define bfilp_cache runtime_const_ptr(__bfilp_cache)
>
> IMO the entire runtime_const_ptr thing for caches is wrong;
> statically allocated kmem_cache series got stalled, but I'm
> bringing it back next cycle and this stuff is going to get
> reverted as part of that.

I'm not going to spend time arguing about this. Given the
aforementioned direction I'm going to refrain from patching up more
caches though.