linux-kernel - Re: [PATCH -mm 2/3] slab: zap kmem_cache

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Message-ID: <alpine.DEB.2.11.1501261427310.17468@gentwo.org>
Date:	Mon, 26 Jan 2015 14:28:33 -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 2/3] slab: zap kmem_cache_shrink return value

On Mon, 26 Jan 2015, Vladimir Davydov wrote:

> Right, but I just don't see why a subsystem using a kmem_cache would
> need to check whether there are any objects left in the cache. I mean,
> it should somehow keep track of the objects it's allocated anyway, e.g.
> by linking them in a list. That means it must already have a way to
> check if it is safe to destroy its cache or not.

The acpi subsystem did that at some point.

> Suppose we leave the return value as is. A subsystem, right before going
> to destroy a cache, calls kmem_cache_shrink, which returns 1 (slab is
> not empty). What is it supposed to do then?

That is up to the subsystem. If it has a means of tracking down the
missing object then it can deal with it. If not then it cannot shutdown
the cache and do a proper recovery action.

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