linux-kernel - Re: [PATCH -mm 3/3] slub: make dead caches discard free slabs immediately

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Date:	Tue, 27 Jan 2015 12:28:39 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Joonsoo Kim <js1304@...il.com>
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	"Linux Memory Management List" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm 3/3] slub: make dead caches discard free slabs
 immediately

On Tue, Jan 27, 2015 at 06:21:14PM +0900, Joonsoo Kim wrote:
> 2015-01-27 17:23 GMT+09:00 Vladimir Davydov <vdavydov@...allels.com>:
> > Hi Joonsoo,
> >
> > On Tue, Jan 27, 2015 at 05:00:09PM +0900, Joonsoo Kim wrote:
> >> On Mon, Jan 26, 2015 at 03:55:29PM +0300, Vladimir Davydov wrote:
> >> > @@ -3381,6 +3390,15 @@ void __kmem_cache_shrink(struct kmem_cache *s)
> >> >             kmalloc(sizeof(struct list_head) * objects, GFP_KERNEL);
> >> >     unsigned long flags;
> >> >
> >> > +   if (deactivate) {
> >> > +           /*
> >> > +            * Disable empty slabs caching. Used to avoid pinning offline
> >> > +            * memory cgroups by freeable kmem pages.
> >> > +            */
> >> > +           s->cpu_partial = 0;
> >> > +           s->min_partial = 0;
> >> > +   }
> >> > +
> >>
> >> Maybe, kick_all_cpus_sync() is needed here since object would
> >> be freed asynchronously so they can't see this updated value.
> >
> > I thought flush_all() should do the trick, no?
> 
> Unfortunately, it doesn't.
> 
> flush_all() sends IPI to not all cpus. It only sends IPI to cpus where
> some conditions
> are met and freeing could occur on the other ones.

Oh, true, missed that. Yeah, we should kick all cpus explicitly then.
Will fix in the next iteration. Thanks for catching this!

Thanks,
Vladimir
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