linux-kernel - Re: [PATCH -mm 1/3] slub: don't fail kmem_cache_shrink if slab placement optimization fails

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Date:	Mon, 26 Jan 2015 12:24:49 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 1/3] slub: don't fail kmem_cache_shrink if slab
 placement optimization fails

On Mon, 26 Jan 2015, Vladimir Davydov wrote:

> Anyways, I think that silently relying on the fact that the allocator
> never fails small allocations is kind of unreliable. What if this

We are not doing that though. If the allocation fails we do nothing.

> > > +			if (page->inuse < objects)
> > > +				list_move(&page->lru,
> > > +					  slabs_by_inuse + page->inuse);
> > >  			if (!page->inuse)
> > >  				n->nr_partial--;
> > >  		}
> >
> > The condition is always true. A page that has page->inuse == objects
> > would not be on the partial list.
> >
>
> This is in case we failed to allocate the slabs_by_inuse array. We only
> have a list for empty slabs then (on stack).

Ok in that case objects == 1. If you want to do this maybe do it in a more
general way?

You could allocate an array on the stack to deal with the common cases. I
believe an array of 32 objects would be fine to allocate and cover most of
the slab caches on the system? Would eliminate most of the allocations in
kmem_cache_shrink.


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