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Date: Mon, 26 Jan 2015 14:28:33 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
Subject: Re: [PATCH -mm 2/3] slab: zap kmem_cache_shrink return value
In-Reply-To: <20150126201602.GA3317@esperanza>
Message-ID: <alpine.DEB.2.11.1501261427310.17468@gentwo.org>
References: <cover.1422275084.git.vdavydov@parallels.com> <b89d28384f8ec7865c3fefc2f025955d55798b78.1422275084.git.vdavydov@parallels.com> <alpine.DEB.2.11.1501260949150.15849@gentwo.org> <20150126170418.GC28978@esperanza> <alpine.DEB.2.11.1501261226250.16638@gentwo.org>
 <20150126194838.GB2660@esperanza> <alpine.DEB.2.11.1501261353480.16786@gentwo.org> <20150126201602.GA3317@esperanza>
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Sender: owner-linux-mm@kvack.org
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To: Vladimir Davydov <vdavydov@parallels.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>, linux-mm@kvack.org, linux-kernel@vger.kernel.org

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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