Re: [patch 21/26] Slab defragmentation: support dentry defragmentation
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2007-06-26 08:22:25
Also in:
lkml
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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