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

Mathieu Desnoyers
2012-10-29T13:23:27Z

* Sasha Levin (levinsasha928@gmail.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@gmail.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.