Messages in this thread | | | Date | Tue, 26 Jun 2007 01:18:45 -0700 | From | Andrew Morton <> | Subject | Re: [patch 21/26] Slab defragmentation: support dentry defragmentation |
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On Mon, 18 Jun 2007 02:58:59 -0700 clameter@sgi.com wrote:
> get() uses the dcache lock and then works with dget_locked to obtain a > reference to the dentry. An additional complication is that the dentry > may be in process of being freed or it may just have been allocated. > We add an additional flag to d_flags to be able to determined the > status of an object. > > kick() is called after get() has been used and after the slab has dropped > all of its own locks. The dentry pruning for unused entries works in a > straighforward way. > > ... > > +/* > + * Slab has dropped all the locks. Get rid of the > + * refcount we obtained earlier and also rid of the > + * object. > + */ > +static void kick_dentries(struct kmem_cache *s, int nr, void **v, void *private) > +{ > + struct dentry *dentry; > + int abort = 0; > + int i; > + > + /* > + * First invalidate the dentries without holding the dcache lock > + */ > + for (i = 0; i < nr; i++) { > + dentry = v[i]; > + > + if (dentry) > + d_invalidate(dentry); > + } > + > + /* > + * If we are the last one holding a reference then the dentries can > + * be freed. We need the dcache_lock. > + */ > + spin_lock(&dcache_lock); > + for (i = 0; i < nr; i++) { > + dentry = v[i]; > + if (!dentry) > + continue; > + > + if (abort) > + goto put_dentry; > + > + spin_lock(&dentry->d_lock); > + if (atomic_read(&dentry->d_count) > 1) { > + /* > + * Reference count was increased. > + * We need to abandon the freeing of > + * objects. > + */ > + abort = 1;
It's unobvious why the entire shrink effort is abandoned if one busy dentry is encountered. Please flesh the comment out explaining this.
> + spin_unlock(&dentry->d_lock); > +put_dentry: > + spin_unlock(&dcache_lock); > + dput(dentry); > + spin_lock(&dcache_lock); > + continue; > + } > + > + /* Remove from LRU */ > + if (!list_empty(&dentry->d_lru)) { > + dentry_stat.nr_unused--; > + list_del_init(&dentry->d_lru); > + } > + /* Drop the entry */ > + prune_one_dentry(dentry, 1); > + } > + spin_unlock(&dcache_lock); > + > + /* > + * dentries are freed using RCU so we need to wait until RCU > + * operations arei complete > + */ > + if (!abort) > + synchronize_rcu(); > +}
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