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

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Date:	Mon, 13 Jul 2015 02:03:58 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	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 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.

Nevermind that we don't ignore any other registration time error in
the kernel.

> > The right way forward is to handle register failure properly.
> 
> In other words, to
>  (a) keep a flag to signify that register was not successful
> or
>  (b) look at ->shrinker.list.next or ->nr_deferred
> or
>  (c) treat register failures as critical errors. (I sort of
>      disagree with you here).

The only important part is here is (c).
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