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From: Oskar Andero <oskar.andero@sonymobile.com>
Date: Mon, 15 Apr 2013 17:03:56 +0200
To: Dan Carpenter <dan.carpenter@oracle.com>
CC: "Dolkow, Snild" <Snild.Dolkow@sonymobile.com>,
        "devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Lekanovic, Radovan" <Radovan.Lekanovic@sonymobile.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Brian Swetland <swetland@google.com>
Subject: Re: [PATCH] lowmemorykiller: prevent multiple instances of low
 memory killer
Message-ID: <20130415150356.GA22161@caracas.corpusers.net>
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On 16:13 Mon 15 Apr     , Dan Carpenter wrote:
> On Mon, Apr 15, 2013 at 03:38:08PM +0200, Dolkow, Snild wrote:
> > >Where is lowmem_shrink called from?  I only see shrink called from the
> > >bcache sysfs handler __bch_cache_set().  The return value isn't checked
> > >there.
> > >
> > >Up to now this function has only returns positive numbers.
> > >
> > >There isn't a place which check LMK_BUSY so maybe it's best to just
> > >return zero?
> > 
> > Hey Dan,
> > 
> > lowmem_shrink is assigned to a shrinker struct
> > (include/linux/shrinker.h) and called in do_shrinker_shrink() in
> > mm/vmscan.c. That, in turn, is called and checked in a few places
> > in vmscan.c.
> >
> > >From the comments in shrinker.h: 
> > "It should return the number of objects which remain in the
> > cache. If it returns -1, it means it cannot do any scanning at
> > this time (eg. there is a risk of deadlock). The callback must not
> > return -1 if nr_to_scan is zero."
> 
> Ah.  Good.  -1 is the right return.
> 
> But really should be a #define in shrinker.h instead of in
> drivers/staging/android/.

IMO one should use the errno.h values - e.g. EBUSY might be a good
value in this case. Does anyone know why the shrinker wants -1? Is there
a reason?

-Oskar