linux-kernel - Re: [PATCH] lowmemorykiller: prevent multiple instances of low memory killer

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Date:	Mon, 15 Apr 2013 16:11:18 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:	"Dolkow, Snild" <Snild.Dolkow@...ymobile.com>,
	Oskar.Andero@...ymobile.com,
	Dan Carpenter <dan.carpenter@...cle.com>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"Lekanovic, Radovan" <Radovan.Lekanovic@...ymobile.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Brian Swetland <swetland@...gle.com>
Subject: Re: [PATCH] lowmemorykiller: prevent multiple instances of low memory
 killer

On Mon, 15 Apr 2013, Greg Kroah-Hartman wrote:

> > The positive numbers are used to return information on the remaining
> > cache size (again, see the comment I pasted above). We could use
> > -EBUSY, but we'd have to change vmscan.c, which checks specifically
> > for -1. I can't see a technical reason why -EBUSY couldn't have been
> > chosen instead, but there's also no real reason to change it now.
> 
> If it's not the correct thing to do, sure we can change it, just send a
> patch.  It makes way more sense than some random -1 return value to me.
> 
> Care to send a series of patches fixing this up properly?
> 

The comment in shrinker.h is misleading, not the source code.  
do_shrinker_shrink() will fail for anything negative and 0.  The patch 
being discussed could easily use -1 or 0 hardcoded into the return value, 
forget the definition of LMK_BUSY.

Also, please consider using an atomic chmpxchg instead of a spinlock: if 
you're only ever doing spin_trylock() then you don't need a spinlock.
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