linux-kernel - Re: [PATCH v7 13/16] lockd: use new hashtable implementation

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Date:	Mon, 29 Oct 2012 09:23:23 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	torvalds@...ux-foundation.org, tj@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v7 13/16] lockd: use new hashtable implementation

* Sasha Levin (levinsasha928@...il.com) wrote:
> Switch lockd to use the new hashtable implementation. This reduces the amount of
> generic unrelated code in lockd.
> 
> Signed-off-by: Sasha Levin <levinsasha928@...il.com>
> ---
>  fs/lockd/svcsubs.c | 66 +++++++++++++++++++++++++++++-------------------------
>  1 file changed, 36 insertions(+), 30 deletions(-)
> 
> diff --git a/fs/lockd/svcsubs.c b/fs/lockd/svcsubs.c
> index 0deb5f6..d223a1f 100644
> --- a/fs/lockd/svcsubs.c
> +++ b/fs/lockd/svcsubs.c
> @@ -20,6 +20,7 @@
>  #include <linux/lockd/share.h>
>  #include <linux/module.h>
>  #include <linux/mount.h>
> +#include <linux/hashtable.h>
>  
>  #define NLMDBG_FACILITY		NLMDBG_SVCSUBS
>  
> @@ -28,8 +29,7 @@
>   * Global file hash table
>   */
>  #define FILE_HASH_BITS		7
> -#define FILE_NRHASH		(1<<FILE_HASH_BITS)
> -static struct hlist_head	nlm_files[FILE_NRHASH];
> +static DEFINE_HASHTABLE(nlm_files, FILE_HASH_BITS);
>  static DEFINE_MUTEX(nlm_file_mutex);
>  
>  #ifdef NFSD_DEBUG
> @@ -68,7 +68,7 @@ static inline unsigned int file_hash(struct nfs_fh *f)
>  	int i;
>  	for (i=0; i<NFS2_FHSIZE;i++)
>  		tmp += f->data[i];
> -	return tmp & (FILE_NRHASH - 1);
> +	return tmp;
>  }
>  
>  /*
> @@ -86,17 +86,17 @@ nlm_lookup_file(struct svc_rqst *rqstp, struct nlm_file **result,
>  {
>  	struct hlist_node *pos;
>  	struct nlm_file	*file;
> -	unsigned int	hash;
> +	unsigned int	key;
>  	__be32		nfserr;
>  
>  	nlm_debug_print_fh("nlm_lookup_file", f);
>  
> -	hash = file_hash(f);
> +	key = file_hash(f);
>  
>  	/* Lock file table */
>  	mutex_lock(&nlm_file_mutex);
>  
> -	hlist_for_each_entry(file, pos, &nlm_files[hash], f_list)
> +	hash_for_each_possible(nlm_files, file, pos, f_list, file_hash(f))

we have a nice example of weirdness about key vs hash here:

1) "key" is computed from file_hash(f)
2) file_hash(f) is computed again and again in hash_for_each_possible()

>  		if (!nfs_compare_fh(&file->f_handle, f))
>  			goto found;
>  
> @@ -123,7 +123,7 @@ nlm_lookup_file(struct svc_rqst *rqstp, struct nlm_file **result,
>  		goto out_free;
>  	}
>  
> -	hlist_add_head(&file->f_list, &nlm_files[hash]);
> +	hash_add(nlm_files, &file->f_list, key);

3) then we use "key" as parameter to hash_add.

Moreover, we're adding dispersion to the file_hash() with the hash_32()
called under the hook within hashtable.h. Is it an intended behavior ?
This should at the very least be documented in the changelog.

[...]

> +static int __init nlm_init(void)
> +{
> +	hash_init(nlm_files);

Useless.

Thanks,

Mathieu

> +	return 0;
> +}
> +
> +module_init(nlm_init);
> -- 
> 1.7.12.4
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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