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

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Date:	Mon, 13 Jul 2015 15:52:53 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH 0/2] mm/shrinker: make unregister_shrinker() less fragile

On (07/12/15 23:33), Christoph Hellwig wrote:
> On Sun, Jul 12, 2015 at 11:47:32AM +0900, Sergey Senozhatsky wrote:
> > Yes, but the main difference here is that it seems that shrinker users
> > don't tend to treat shrinker registration failures as fatal errors and
> > just continue with shrinker functionality disabled. And it makes sense.
> > 
> > (copy paste from https://lkml.org/lkml/2015/7/9/751)
> > 
> 
> I hearily disagree.  It's not any less critical than other failures.

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).

> 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).

	-ss
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