Re: [Xen-devel] [PATCH] xen-blkback: fix memory leak when persistent grants are used

[Ian Campbell <Ian.Campbell@citrix.com>]

On Sat, 2014-01-25 at 13:07 -0800, Matt Wilson wrote:
> On Fri, Jan 24, 2014 at 03:36:22PM +0000, Ian Campbell wrote:
> > On Fri, 2014-01-24 at 09:21 +0000, Ian Campbell wrote:
> > > On Thu, 2014-01-23 at 11:28 -0800, Matt Wilson wrote:
> > > > From: Matt Rushton <mrushton@amazon.com>
> > > > 
> > > > Currently shrink_free_pagepool() is called before the pages used for
> > > > persistent grants are released via free_persistent_gnts(). This
> > > > results in a memory leak when a VBD that uses persistent grants is
> > > > torn down.
> > > 
> > > This may well be the explanation for the memory leak I was observing on
> > > ARM last night. I'll give it a go and let you know.
> > 
> > Results are a bit inconclusive unfortunately, it seems like I am seeing
> > some other leak too (or instead).
> > 
> > Totally unscientifically it does seem to be leaking more slowly than
> > before, so perhaps this patch has helped, but nothing conclusive I'm
> > afraid.
> 
> Testing here looks good. I don't know if perhaps something else is
> going on with ARM...
> 
> > I don't think that quite qualifies for a Tested-by though, sorry.
> 
> How about an Acked-by? ;-)

I'm not at all familiar with the modern blkback code base so I'm afraid
it would be a pretty hollow Ack.

> 
> --msw
> 
> > Ian. 
> > 
> > > 
> > > > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > > > Cc: "Roger Pau Monné" <roger.pau@citrix.com>
> > > > Cc: Ian Campbell <Ian.Campbell@citrix.com>
> > > > Cc: David Vrabel <david.vrabel@citrix.com>
> > > > Cc: linux-kernel@vger.kernel.org
> > > > Cc: xen-devel@lists.xen.org
> > > > Cc: Anthony Liguori <aliguori@amazon.com>
> > > > Signed-off-by: Matt Rushton <mrushton@amazon.com>
> > > > Signed-off-by: Matt Wilson <msw@amazon.com>
> > > > ---
> > > >  drivers/block/xen-blkback/blkback.c |    6 +++---
> > > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> > > > index 6620b73..30ef7b3 100644
> > > > --- a/drivers/block/xen-blkback/blkback.c
> > > > +++ b/drivers/block/xen-blkback/blkback.c
> > > > @@ -625,9 +625,6 @@ purge_gnt_list:
> > > >  			print_stats(blkif);
> > > >  	}
> > > >  
> > > > -	/* Since we are shutting down remove all pages from the buffer */
> > > > -	shrink_free_pagepool(blkif, 0 /* All */);
> > > > -
> > > >  	/* Free all persistent grant pages */
> > > >  	if (!RB_EMPTY_ROOT(&blkif->persistent_gnts))
> > > >  		free_persistent_gnts(blkif, &blkif->persistent_gnts,
> > > > @@ -636,6 +633,9 @@ purge_gnt_list:
> > > >  	BUG_ON(!RB_EMPTY_ROOT(&blkif->persistent_gnts));
> > > >  	blkif->persistent_gnt_c = 0;
> > > >  
> > > > +	/* Since we are shutting down remove all pages from the buffer */
> > > > +	shrink_free_pagepool(blkif, 0 /* All */);
> > > > +
> > > >  	if (log_stats)
> > > >  		print_stats(blkif);
> > > >  
> > > 
> > > 
> > > 
> > > _______________________________________________
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> > > Xen-devel@lists.xen.org
> > > http://lists.xen.org/xen-devel
> > 
> >