linux-kernel - Re: [PATCH] fs: filp_cachep can be static in fs/file

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Date:	Wed, 10 Dec 2008 09:35:45 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs: filp_cachep can be static in fs/file_table.c

On Tue, Dec 09, 2008 at 11:48:45PM +0100, Eric Dumazet wrote:
> Hi Andrew
> 
> Please find two cleanups before patch re-submission to use
> SLAB_DESTROY_BY_RCU for "struct file".
> 
> Thank you
> 
> [PATCH] fs: filp_cachep can be static in fs/file_table.c
> 
> 1) Documentation cleanup
> 
> Documentation/filesystems/files.txt was not updated when
> f_count became an atomic_long_t.
> atomic_long_inc_not_zero() is now used instead of atomic_inc_not_zero()
> 
> 2) filp_cachep can be static to fs/file_table.c
> 
> Instead of creating the "filp" kmem_cache in vfs_caches_init(),
> we can do it a litle be later in files_init(), so that filp_cachep
> is static to fs/file_table.c

Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
> ---
>  Documentation/filesystems/files.txt |    6 +++---
>  fs/dcache.c                         |    6 ------
>  fs/file_table.c                     |   10 +++++++++-
>  include/linux/fdtable.h             |    2 --
>  4 files changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/Documentation/filesystems/files.txt b/Documentation/filesystems/files.txt
> index bb0142f..ac2facc 100644
> --- a/Documentation/filesystems/files.txt
> +++ b/Documentation/filesystems/files.txt
> @@ -76,13 +76,13 @@ the fdtable structure -
>  5. Handling of the file structures is special. Since the look-up
>     of the fd (fget()/fget_light()) are lock-free, it is possible
>     that look-up may race with the last put() operation on the
> -   file structure. This is avoided using atomic_inc_not_zero()
> +   file structure. This is avoided using atomic_long_inc_not_zero()
>     on ->f_count :
> 
>  	rcu_read_lock();
>  	file = fcheck_files(files, fd);
>  	if (file) {
> -		if (atomic_inc_not_zero(&file->f_count))
> +		if (atomic_long_inc_not_zero(&file->f_count))
>  			*fput_needed = 1;
>  		else
>  		/* Didn't get the reference, someone's freed */
> @@ -92,7 +92,7 @@ the fdtable structure -
>  	....
>  	return file;
> 
> -   atomic_inc_not_zero() detects if refcounts is already zero or
> +   atomic_long_inc_not_zero() detects if refcounts is already zero or
>     goes to zero during increment. If it does, we fail
>     fget()/fget_light().
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index a1d86c7..fa1ba03 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -2313,9 +2313,6 @@ static void __init dcache_init(void)
>  /* SLAB cache for __getname() consumers */
>  struct kmem_cache *names_cachep __read_mostly;
> 
> -/* SLAB cache for file structures */
> -struct kmem_cache *filp_cachep __read_mostly;
> -
>  EXPORT_SYMBOL(d_genocide);
> 
>  void __init vfs_caches_init_early(void)
> @@ -2337,9 +2334,6 @@ void __init vfs_caches_init(unsigned long mempages)
>  	names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
>  			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
> 
> -	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
> -			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
> -
>  	dcache_init();
>  	inode_init();
>  	files_init(mempages);
> diff --git a/fs/file_table.c b/fs/file_table.c
> index 5ad0eca..a46e880 100644
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -32,6 +32,9 @@ struct files_stat_struct files_stat = {
>  /* public. Not pretty! */
>  __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
> 
> +/* SLAB cache for file structures */
> +static struct kmem_cache *filp_cachep __read_mostly;
> +
>  static struct percpu_counter nr_files __cacheline_aligned_in_smp;
> 
>  static inline void file_free_rcu(struct rcu_head *head)
> @@ -397,7 +400,12 @@ too_bad:
>  void __init files_init(unsigned long mempages)
>  { 
>  	int n; 
> -	/* One file with associated inode and dcache is very roughly 1K. 
> +
> +	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
> +			SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
> +
> +	/*
> +	 * One file with associated inode and dcache is very roughly 1K. 
>  	 * Per default don't use more than 10% of our memory for files. 
>  	 */ 
> 
> diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
> index 4aab6f1..09d6c5b 100644
> --- a/include/linux/fdtable.h
> +++ b/include/linux/fdtable.h
> @@ -57,8 +57,6 @@ struct files_struct {
> 
>  #define files_fdtable(files) (rcu_dereference((files)->fdt))
> 
> -extern struct kmem_cache *filp_cachep;
> -
>  struct file_operations;
>  struct vfsmount;
>  struct dentry;
> --
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