Re: [RFC][PATCH 2/9] deadlock prevention core

From: Peter Zijlstra
Date: Tue Aug 08 2006 - 17:03:51 EST

On Tue, 2006-08-08 at 13:57 -0700, Stephen Hemminger wrote:
> On Tue, 08 Aug 2006 21:33:45 +0200
> Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> >
> > The core of the VM deadlock avoidance framework.
> >
> > From the 'user' side of things it provides a function to mark a 'struct sock'
> > as SOCK_MEMALLOC, meaning this socket may dip into the memalloc reserves on
> > the receive side.
> >
> > From the net_device side of things, the extra 'struct net_device *' argument
> > to {,__}netdev_alloc_skb() is used to attribute/account the memalloc usage.
> > Converted drivers will make use of this new API and will set NETIF_F_MEMALLOC
> > to indicate the driver fully supports this feature.
> >
> > When a SOCK_MEMALLOC socket is marked, the device is checked for this feature
> > and tries to increase the memalloc pool; if both succeed, the device is marked
> > with IFF_MEMALLOC, indicating to {,__}netdev_alloc_skb() that it is OK to dip
> > into the memalloc pool.
> >
> > Memalloc sk_buff allocations are not done from the SLAB but are done using
> > alloc_pages(). sk_buff::memalloc records this exception so that kfree_skbmem()
> > can do the right thing.
> >
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > Signed-off-by: Daniel Phillips <phillips@xxxxxxxxxx>
> >
> How much of this is just building special case support for large allocations
> for jumbo frames? Wouldn't it make more sense to just fix those drivers to
> do scatter and add the support hooks for that?

Only some of the horrors in __alloc_skb(), esp those related to the
order argument. OTOH, yes I would very much like all the jumbo capable
driver to do proper scather/gather on fragments, alas drivers are not my
storng point.

If someone (preferably the maintainers) will contribute patches....

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