netdev - Re: ipw2200: firmware DMA loading rework

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Date:	Tue, 08 Sep 2009 22:39:26 +0200
From:	Simon Kitching <simon.kitching@...llo.at>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Theodore Tso <tytso@....edu>,
	"Luis R. Rodriguez" <mcgrof@...il.com>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Zhu Yi <yi.zhu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Mel Gorman <mel@...net.ie>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	James Ketrenos <jketreno@...ux.intel.com>,
	"Chatre, Reinette" <reinette.chatre@...el.com>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"ipw2100-devel@...ts.sourceforge.net" 
	<ipw2100-devel@...ts.sourceforge.net>
Subject: Re: ipw2200: firmware DMA loading rework

On Tue, 2009-09-08 at 12:00 +0100, Mel Gorman wrote:
> On Sat, Sep 05, 2009 at 10:28:37AM -0400, Theodore Tso wrote:
> > On Thu, Sep 03, 2009 at 01:49:14PM +0100, Mel Gorman wrote:
> > > > 
> > > > This looks very similar to the kmemleak ext4 reports upon a mount. If
> > > > it is the same issue, which from the trace it seems it is, then this
> > > > is due to an extra kmalloc() allocation and this apparently will not
> > > > get fixed on 2.6.31 due to the closeness of the merge window and the
> > > > non-criticalness this issue has been deemed.
> > 
> > No, it's a different problem.
> > 
> > > I suspect the more pressing concern is why is this kmalloc() resulting in
> > > an order-5 allocation request? What size is the buffer being requested?
> > > Was that expected?  What is the contents of /proc/slabinfo in case a buffer
> > > that should have required order-1 or order-2 is using a higher order for
> > > some reason.
> > 
> > It's allocating 68,000 bytes for the mb_history structure, which is
> > used for debugging purposes.  That's why it's optional and we continue
> > if it's not allocated.  We should fix it to use vmalloc()
> 
> You could call with kmalloc(FLAGS|GFP_NOWARN) with a fallback to
> vmalloc() and a disable if vmalloc() fails as well.  Maybe check out what
> kernel/profile.c#profile_init() to allocate a large buffer and do something
> similar?
> 
> > and I'm
> > inclined to turn it off by default since it's not worth the overhead,
> > and most ext4 users won't find it useful or interesting.
> > 
> 
> I can't comment as I don't know what sort of debugging it's useful for.
> 

Perhaps this is a suitable use for the new proposed flex_array? From an
initial glance, I can't see why the allocated memory has to be
contiguous..

http://lwn.net/Articles/345273/

Cheers, Simon

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