Re: [patch 20/23] dentries: Add constructor

Mel Gorman
2007-11-08T15:23:36Z

On (06/11/07 17:11), Christoph Lameter didst pronounce:
> In order to support defragmentation on the dentry cache we need to have
> a determined object state at all times. Without a constructor the object
> would have a random state after allocation.
>
> Reviewed-by: Rik van Riel <riel@redhat.com>
> So provide a constructor.
>
> Signed-off-by: Christoph Lameter <clameter@sgi.com>

Seems to be some garbling on there in the signed-off lines.

> ---
> fs/dcache.c | 26 ++++++++++++++------------
> 1 file changed, 14 insertions(+), 12 deletions(-)
>
> Index: linux-2.6/fs/dcache.c
> ===================================================================
> --- linux-2.6.orig/fs/dcache.c 2007-11-06 12:56:56.000000000 -0800
> +++ linux-2.6/fs/dcache.c 2007-11-06 12:57:01.000000000 -0800
> @@ -870,6 +870,16 @@ static struct shrinker dcache_shrinker =
> .seeks = DEFAULT_SEEKS,
> };
>
> +void dcache_ctor(struct kmem_cache *s, void *p)
> +{
> + struct dentry *dentry = p;
> +
> + spin_lock_init(&dentry->d_lock);
> + dentry->d_inode = NULL;
> + INIT_LIST_HEAD(&dentry->d_lru);
> + INIT_LIST_HEAD(&dentry->d_alias);
> +}
> +

Is there any noticable overhead to the constructor?

> /**
> * d_alloc - allocate a dcache entry
> * @parent: parent of entry to allocate
> @@ -907,8 +917,6 @@ struct dentry *d_alloc(struct dentry * p
>
> atomic_set(&dentry->d_count, 1);
> dentry->d_flags = DCACHE_UNHASHED;
> - spin_lock_init(&dentry->d_lock);
> - dentry->d_inode = NULL;
> dentry->d_parent = NULL;
> dentry->d_sb = NULL;
> dentry->d_op = NULL;
> @@ -918,9 +926,7 @@ struct dentry *d_alloc(struct dentry * p
> dentry->d_cookie = NULL;
> #endif
> INIT_HLIST_NODE(&dentry->d_hash);
> - INIT_LIST_HEAD(&dentry->d_lru);
> INIT_LIST_HEAD(&dentry->d_subdirs);
> - INIT_LIST_HEAD(&dentry->d_alias);
>
> if (parent) {
> dentry->d_parent = dget(parent);
> @@ -2096,14 +2102,10 @@ static void __init dcache_init(void)
> {
> int loop;
>
> - /*
> - * A constructor could be added for stable state like the lists,
> - * but it is probably not worth it because of the cache nature
> - * of the dcache.
> - */
> - dentry_cache = KMEM_CACHE(dentry,
> - SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
> -
> + dentry_cache = kmem_cache_create("dentry_cache", sizeof(struct dentry),
> + 0, SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD,
> + dcache_ctor);
> +
> register_shrinker(&dcache_shrinker);
>
> /* Hash may have been set up in dcache_init_early */

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab