Re: 2.5.39 kmem_cache bug

Ed Tomlinson (tomlins@cam.org)
Sun, 29 Sep 2002 09:15:52 -0400


On September 28, 2002 04:56 pm, Andrew Morton wrote:
> John Levon wrote:
> > kmem_cache_destroy() is falsely reporting
> > "kmem_cache_destroy: Can't free all objects" in 2.5.39. I have
> > verified my code was freeing all allocated items correctly.
> >
> > Reverting this chunk :
> >
> > - list_add(&slabp->list, &cachep->slabs_free);
> > +/* list_add(&slabp->list, &cachep->slabs_free);
> > */ + if
> > (unlikely(list_empty(&cachep->slabs_partial))) +
> > list_add(&slabp->list, &cachep->slabs_partial); +
> > else
> > + kmem_slab_destroy(cachep, slabp);
> >
> > and the problem goes away. I haven't investigated why.
>
> Thanks. That's the code which leaves one empty page available
> for new allocations rather than freeing it immediately.
>
> It's temporary. Ed, I think we can just do
>
> if (list_empty(&cachep->slabs_free))
> list_add(&slabp->list, &cachep->slabs_free);
> else
> kmem_slab_destroy(cachep, slabp);
>
> there?

How about this (untested) instead. If we can avoid using cachep->slabs_free its
a good thing. Why use three lists when two can do the job? I use a loop to clean
the partial list since its possible that for some caches we may want to have more
than one slabp of buffer.

Thoughts?
Ed

---------
diff -Nru a/mm/slab.c b/mm/slab.c
--- a/mm/slab.c Sun Sep 29 09:08:53 2002
+++ b/mm/slab.c Sun Sep 29 09:08:53 2002
@@ -1036,7 +1036,26 @@
list_del(&cachep->next);
up(&cache_chain_sem);

- if (__kmem_cache_shrink(cachep)) {
+ /* remove any empty partial pages */
+ spin_lock_irq(&cachep->spinlock);
+ while (!cachep->growing) {
+ struct list_head *p;
+ slab_t *slabp;
+
+ p = cachep->slabs_partial.prev;
+ if (p == &cachep->slabs_partial)
+ break;
+
+ slabp = list_entry(cachep->slabs_partial.prev, slab_t, list);
+ if (slabp->inuse)
+ break;
+
+ list_del(&slabp->list);
+
+ }
+ spin_unlock_irq(&cachep->spinlock);
+
+ if (!list_empty(&cachep->slabs_full) || !list_empty(&cachep->slabs_partial)) {
printk(KERN_ERR "kmem_cache_destroy: Can't free all objects %p\n",
cachep);
down(&cache_chain_sem);

---------

-
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