Re: [REGRESSION] [FIXED] [PATCH 1/3] mm/slab: use percpu allocator for cpu cache

[Jeremiah Mahler]

Joonsoo,

On Mon, Sep 29, 2014 at 04:44:18PM +0900, Joonsoo Kim wrote:
> On Sat, Sep 27, 2014 at 11:24:49PM -0700, Jeremiah Mahler wrote:
> > On Thu, Aug 21, 2014 at 05:11:13PM +0900, Joonsoo Kim wrote:
> > > Because of chicken and egg problem, initializaion of SLAB is really
> > > complicated. We need to allocate cpu cache through SLAB to make
> > > the kmem_cache works, but, before initialization of kmem_cache,
> > > allocation through SLAB is impossible.
> > > 
> > > On the other hand, SLUB does initialization with more simple way. It
> > > uses percpu allocator to allocate cpu cache so there is no chicken and
> > > egg problem.
> > > 
> > > So, this patch try to use percpu allocator in SLAB. This simplify
> > > initialization step in SLAB so that we could maintain SLAB code more
> > > easily.
> > > 
> > > From my testing, there is no performance difference.
> > > 
> > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > 
> > I just encountered a problem on a Lenovo Carbon X1 where it will
> > suspend but won't resume.  A bisect indicated that this patch
> > is causing the problem.
> > 
> > 997888488ef92da365b870247de773255227ce1f
> > 
> > I imagine the patch author, Joonsoo Kim, might have a better idea
> > why this is happening than I do.  But if I can provide any information
> > or run any tests that might be of help just let me know.
> 
> Hello,
> 
> Yeah, there is a bug. Below will fix your issue.
> Could you test it and report the result?
> 
> Thanks for reporting it.
> 
> --------->8---------------
> From e03ed6cc554e038b86d7b3a72b89d94e9ea808ba Mon Sep 17 00:00:00 2001
> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Date: Mon, 29 Sep 2014 16:30:43 +0900
> Subject: [PATCH] mm/slab: fix cpu on/off handling
> 
> When cpu off, we flush all cpu cached objects to it's own slab.
> free_block() is used for this purpose and it's role is just to flush
> objects from array_cache to proper slab. It doesn't adjust array_cache's
> internal fields so we should manually reset them to proper value.
> Without this fix, we maintain free objects duplicately, one is in
> cpu cache, and, the other one is in the slab. So system would be broken.
> 
> Reported-by: Jeremiah Mahler <jmmahler@xxxxxxxxx>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> ---
>  mm/slab.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index 1162f0e..ce289b4 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1102,8 +1102,10 @@ static void cpuup_canceled(long cpu)
>  
>  		/* cpu is dead; no one can alloc from it. */
>  		nc = per_cpu_ptr(cachep->cpu_cache, cpu);
> -		if (nc)
> +		if (nc) {
>  			free_block(cachep, nc->entry, nc->avail, node, &list);
> +			nc->avail = 0;
> +		}
>  
>  		if (!cpumask_empty(mask)) {
>  			spin_unlock_irq(&n->list_lock);
> -- 
> 1.7.9.5
> 

That fixed the problem.  Thanks!

Tested-by: Jeremiah Mahler <jmmahler@xxxxxxxxx>

-- 
Jeremiah Mahler
jmmahler@xxxxxxxxx
http://github.com/jmahler
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