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Date: Tue, 14 Jul 2015 00:17:59 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] mm/shrinker: make unregister_shrinker() less fragile
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On Mon, Jul 13, 2015 at 06:34:42PM +0900, Sergey Senozhatsky wrote:
> Yes. 'Nice' used in a sense that drivers have logic to release the
> memory anyway; mm asks volunteers (the drivers that have registered
> shrinker callbacks) to release some spare/wasted/etc. when things
> are getting tough (the drivers are not aware of that in general).
> This is surely important to mm, not to the driver though -- it just
> agrees to be 'nice', but even not expected to release any memory at
> all (IOW, this is not a contract).

Not registering the shrinker is a plain and simple memory leak.  Just
like a missing free your driver will appear to work fine for a while,
but eventually the leaks will bring down the whole system including
your driver.