netdev - Re: [PATCH net-next] xen-netback: allocate xenvif arrays using vzalloc.

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Message-ID: <1383089055.4176.1.camel@edumazet-glaptop.roam.corp.google.com>
Date:	Tue, 29 Oct 2013 16:24:15 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Joby Poriyath <joby.poriyath@...rix.com>
Cc:	netdev@...r.kernel.org, wei.liu2@...rix.com,
	ian.campbell@...rix.com, xen-devel@...ts.xen.org,
	andrew.bennieston@...rix.com, david.vrabel@...rix.com,
	malcolm.crossley@...rix.com
Subject: Re: [PATCH net-next] xen-netback: allocate xenvif arrays using
 vzalloc.

On Tue, 2013-10-29 at 18:46 +0000, Joby Poriyath wrote:
> On Tue, Oct 29, 2013 at 08:43:50AM -0700, Eric Dumazet wrote:
> > On Tue, 2013-10-29 at 15:27 +0000, Joby Poriyath wrote:
> > > This will reduce memory pressure when allocating struct xenvif.
> > > 
> > > The size of xenvif struct has increased from 168 to 36632 bytes (on x86-32).
> > > See commit b3f980bd827e6e81a050c518d60ed7811a83061d. This resulted in
> > > occasional netdev allocation failure in dom0 with 752MiB RAM, due to
> > > fragmented memory.
> > 
> > This looks overkill. 
> > 
> > Replacing a single allocation of ~36 KB into 5 vmalloc() looks like you
> > did not really tried other things...
> > 
> > This should be done generically in alloc_netdev_mqs()
> 
> Sorry Eric, I didn't quite understand how this can be generically done.
> 
> The netback interfaces are tied to the Xen guests (VMs) and these are created 
> when guests are started and deleted when guest are halted.

They are created by alloc_netdev_mqs()

> 
> > 
> > Take a look at commit 60877a32bce00041
> > ("net: allow large number of tx queues")
> > 
> 
> I could try allocating using kmalloc and if that fails, then fall back
> to vmalloc.

My point is the patch should be done in net/core, not in your driver.





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