linux-kernel - Re: [PATCH 0/2] mm/shrinker: make unregister

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Date:	Mon, 13 Jul 2015 18:34:42 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] mm/shrinker: make unregister_shrinker() less fragile

On (07/13/15 02:03), Christoph Hellwig wrote:
> On Mon, Jul 13, 2015 at 03:52:53PM +0900, Sergey Senozhatsky wrote:
> > Why? In some sense, shrinker callbacks are just a way to be nice.
> > No one writes a driver just to be able to handle shrinker calls. An
> > ability to react to those calls is just additional option; it does
> > not directly affect or limit driver's functionality (at least, it
> > really should not).
> 
> No, they are not just nice.  They are a fundamental part of memory
> management and required to reclaim (often large) amounts of memory.

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).

	-ss
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