linux-kernel - Re: [PATCH] slub: Do not assert not having lock in removing freed partial

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Message-ID: <20140205200632.021dc613@gandalf.local.home>
Date:	Wed, 5 Feb 2014 20:06:32 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...nel.org>,
	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] slub: Do not assert not having lock in removing freed
 partial

On Wed, 5 Feb 2014 16:46:43 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:


> > +/*
> > + * The difference between remove_partial and remove_freed_partial
> > + * is that remove_freed_partial happens only on a a freed slab
> 
> Duplicate "a" there.

oops.

> 
> > + * that should not have anyone accessing it, and thus does not
> > + * require the n->list_lock.
> > + */
> > +static inline void remove_freed_partial(struct kmem_cache_node *n,
> > +					struct page *page)
> > +{
> > +	__remove_partial(n, page);
> >  }
> >  
> >  /*
> > @@ -3195,7 +3212,7 @@ static void free_partial(struct kmem_cac
> >  
> >  	list_for_each_entry_safe(page, h, &n->partial, lru) {
> >  		if (!page->inuse) {
> > -			remove_partial(n, page);
> > +			remove_freed_partial(n, page);
> >  			discard_slab(s, page);
> >  		} else {
> >  			list_slab_objects(s, page,
> 
> We'll want to do something similiar for the add_partial() called from
> early_kmem_cache_node_alloc(), right?  It had the added n->list_lock for 
> the same reason and is done during early init where nobody else can be 
> referencing a kmem_cache_node.
> 
> It would probably be better to define these in terms of "partial slabs 
> that cannot have anyone else accessing it" rather than "freed slabs".

Perhaps then we just use the __remove_partial() and __add_partial()
that does not do the checks. That's common practice to use a "__" to
denote that it's special and usually doesn't require locking.

-- Steve
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