linux-kernel - Re: [PATCH 20/20] iscsi: support for swapping over iSCSI.

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Date:	Thu, 14 Sep 2006 22:46:56 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Mike Christie <michaelc@...wisc.edu>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>,
	David Miller <davem@...emloft.net>,
	Rik van Riel <riel@...hat.com>,
	Daniel Phillips <phillips@...gle.com>
Subject: Re: [PATCH 20/20] iscsi: support for swapping over iSCSI.

On Thu, 2006-09-14 at 22:35 +0200, Peter Zijlstra wrote:
> On Thu, 2006-09-14 at 14:22 -0500, Mike Christie wrote:

> > > I thought I found allocations in that path, lemme search...
> > > found this:
> > > 
> > > iscsi_tcp_data_recv()
> > >   iscsi_data_rescv()
> > >     iscsi_complete_pdu()
> > >       __iscsi_complete_pdu()
> > >         iscsi_recv_pdu()
> > >           alloc_skb( GFP_ATOMIC);
> > > 
> > 
> > You are right that is for the netlink interface. Could we move the
> > PF_MEMALLOC setting and clearing to iscsi_recv_pdu and and add it to
> > iscsi_conn_error in scsi_transport_iscsi.c so that iscsi_iser and
> > qla4xxx will have it set when they need it. I will send a patch for this
> > along with a way to have the netlink sock vmio set for all iscsi drivers
> > that need it.
> 
> I already have such a patch, look at:
> http://programming.kicks-ass.net/kernel-patches/vm_deadlock/current/iscsi_vmio.patch
> 
> but what conditional do you want to use for PF_MEMALLOC, an
> unconditional setting will be highly unpopular.
> 
> Hmm, perhaps you could key it of sk_has_vmio(nls)...

On second thought, not such a good idea, that will still be too course.
You only want to force feed stuff originating from
sk_has_vmio(iscsi_tcp_conn->sock->sk) connections, not all
connectections as soon as there is a swapper in the system.

In order to preserve that information you need extra state, abusing this
process flags is as good as propagating __GFP_EMERGENCY down the call
chain with extra gfp_t arguments, perhaps even better, since it will
make sure we catch all allocations.



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