linux-kernel - Re: [PATCH] mm: vmscan: handle any negative return value from scan

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Message-ID: <20130516115212.GC11167@devil.localdomain>
Date:	Thu, 16 May 2013 21:52:12 +1000
From:	Dave Chinner <dchinner@...hat.com>
To:	Oskar Andero <oskar.andero@...ymobile.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Radovan Lekanovic <radovan.lekanovic@...ymobile.com>,
	David Rientjes <rientjes@...gle.com>,
	Glauber Costa <glommer@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] mm: vmscan: handle any negative return value from
 scan_objects

On Thu, May 16, 2013 at 10:42:16AM +0200, Oskar Andero wrote:
> The shrinkers must return -1 to indicate that it is busy. Instead, treat
> any negative value as busy.

Why? The API defines return condition for aborting a scan and gives
a specific value for doing that. i.e. explain why should change the
API to over-specify the 'abort scan" return value like this.

FWIW, using "any" negative number for "abort scan" is a bad API
design decision. It means that in future we can't introduce
different negative return values in the API if we have a new to.
i.e. each specific negative return value needs to have the potential
for defining a different behaviour. 

So if any change needs to be made, it is to change the -1 return
value to an enum and have the shrinkers return that enum when they
want an abort.

-Dave.
-- 
Dave Chinner
dchinner@...hat.com
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