Re: [PATCH] dma-buf: make dma_fence structure a bit smaller v2

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Aug 08, 2019 at 04:41:39PM +0200, Christian König wrote:
> Daniel any more comments on this one?

It's not kerneldoc, but then all the dma-* docs need some serious love
anyway, so all good with me.
-Daniel

> 
> If not I'm going to push it.
> 
> Christian.
> 
> Am 08.08.19 um 15:22 schrieb Christian König:
> > We clear the callback list on kref_put so that by the time we
> > release the fence it is unused. No one should be adding to the cb_list
> > that they don't themselves hold a reference for.
> > 
> > This small change is actually making the structure 16% smaller.
> > 
> > v2: add the comment to the code as well.
> > 
> > Signed-off-by: Christian König <christian.koenig@amd.com>
> > Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> > ---
> >   include/linux/dma-fence.h | 10 ++++++++--
> >   1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> > index 05d29dbc7e62..bea1d05cf51e 100644
> > --- a/include/linux/dma-fence.h
> > +++ b/include/linux/dma-fence.h
> > @@ -65,8 +65,14 @@ struct dma_fence_cb;
> >   struct dma_fence {
> >   	struct kref refcount;
> >   	const struct dma_fence_ops *ops;
> > -	struct rcu_head rcu;
> > -	struct list_head cb_list;
> > +	/* We clear the callback list on kref_put so that by the time we
> > +	 * release the fence it is unused. No one should be adding to the cb_list
> > +	 * that they don't themselves hold a reference for.
> > +	 */
> > +	union {
> > +		struct rcu_head rcu;
> > +		struct list_head cb_list;
> > +	};
> >   	spinlock_t *lock;
> >   	u64 context;
> >   	u64 seqno;
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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