linux-kernel - Re: [Xen-devel] [PATCH net-next v7 4/9] xen-netback: Introduce TX grant mapping

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Message-ID: <20140313111322.GB16807@zion.uk.xensource.com>
Date:	Thu, 13 Mar 2014 11:13:22 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	Zoltan Kiss <zoltan.kiss@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <jonathan.davies@...rix.com>,
	<wei.liu2@...rix.com>, <linux-kernel@...r.kernel.org>,
	<netdev@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH net-next v7 4/9] xen-netback: Introduce TX
 grant mapping

On Thu, Mar 13, 2014 at 11:02:35AM +0000, Ian Campbell wrote:
> On Thu, 2014-03-13 at 10:56 +0000, David Vrabel wrote:
> > On 13/03/14 10:33, Ian Campbell wrote:
> > > On Thu, 2014-03-06 at 21:48 +0000, Zoltan Kiss wrote:
> > >> @@ -135,13 +146,31 @@ struct xenvif {
> > >>  	pending_ring_idx_t pending_cons;
> > >>  	u16 pending_ring[MAX_PENDING_REQS];
> > >>  	struct pending_tx_info pending_tx_info[MAX_PENDING_REQS];
> > >> +	grant_handle_t grant_tx_handle[MAX_PENDING_REQS];
> > >>  
> > >>  	/* Coalescing tx requests before copying makes number of grant
> > >>  	 * copy ops greater or equal to number of slots required. In
> > >>  	 * worst case a tx request consumes 2 gnttab_copy.
> > >>  	 */
> > >>  	struct gnttab_copy tx_copy_ops[2*MAX_PENDING_REQS];
> > >> -
> > >> +	struct gnttab_map_grant_ref tx_map_ops[MAX_PENDING_REQS];
> > >> +	struct gnttab_unmap_grant_ref tx_unmap_ops[MAX_PENDING_REQS];
> > > 
> > > I wonder if we should break some of these arrays into separate
> > > allocations? Wasn't there a problem with sizeof(struct xenvif) at one
> > > point?
> > 
> > alloc_netdev() falls back to vmalloc() if the kmalloc failed so there's
> > no need to split these structures.
> 
> Is vmalloc space in abundant supply? For some reason I thought it was
> limited (maybe that's a 32-bit only limitation?)

32-bit has a limitation of 128MB by default. 64-bit has much larger
address space.

Wei.
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