linux-kernel - Re: [PATCH v2] mm/slub: Run free_partial() outside of the kmem_cache_node->list

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Date:	Tue, 9 Aug 2016 16:52:13 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Safonov <dsafonov@...tuozzo.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dave Gordon <david.s.gordon@...el.com>, linux-mm@...ck.org
Subject: Re: [PATCH v2] mm/slub: Run free_partial() outside of the
 kmem_cache_node->list_lock

On Tue, Aug 09, 2016 at 06:45:39PM +0300, Vladimir Davydov wrote:
> On Tue, Aug 09, 2016 at 04:27:46PM +0100, Chris Wilson wrote:
> ...
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 825ff45..58f0eb6 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -3479,6 +3479,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
> >   */
> >  static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
> >  {
> > +	LIST_HEAD(partial_list);
> 
> nit: slabs added to this list are not partially used - they are free, so
> let's call it 'free_slabs' or 'discard_list' or just 'discard', please

Ok.

> >  	struct page *page, *h;
> >  
> >  	BUG_ON(irqs_disabled());
> > @@ -3486,13 +3487,16 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
> >  	list_for_each_entry_safe(page, h, &n->partial, lru) {
> >  		if (!page->inuse) {
> >  			remove_partial(n, page);
> > -			discard_slab(s, page);
> > +			list_add(&page->lru, &partial_list);
> 
> If there are objects left in the cache on destruction, the cache won't
> be destroyed. Instead it will be left on the slab_list and can get
> reused later. So we should use list_move() here to always leave
> n->partial in a consistent state, even in case of a leak.

Since remove_partial() does an unconditional list_del(),
I presume you want to perform the list_move() even if we hit the error
path, right?
i.e.

    list_for_each_entry_safe(page, h, &n->partial, lru) {
                if (!page->inuse) {
                        remove_partial(n, page);
-                       list_add(&page->lru, &partial_list);
                } else {
                        list_slab_objects(s, page,
                        "Objects remaining in %s on __kmem_cache_shutdown()");
                }
+               list_move(&page->lru, &discard);

-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre