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

[Mike Christie <michaelc@cs.wisc.edu>]

Mike Christie wrote:
> Peter Zijlstra wrote:
>> 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.
>>
> 
> You can move the iscsi_session->swapper field to the iscsi_cls_session
> and have iscsi_swapdev take a iscsi_cls_session and set that flag.
> iscsi_recv_pdu and iscsi_conn_error and all the llds can then access
> this bit.
> 
>> 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.
>>

Oh yeah, on the send side we also allocate some memory for the netlink
interface if there is a connection error (iscsi_conn_failure ->
iscsi_conn_error). And when that is called from the transmit side we can
change the GFP_ATOMICs to GFP_NOIOs since we have process context.

So I am just saying we need to set that flag in a couple more places (if
you set it in iscsi_conn_error if iscsi_cls_session->swapper is set then
don't worry about it), and that I need to change iscsi_conn_failure and
iscsi_conn_error to take a gfp_t as an argument (or do a in_interrupt or
something) so we can use GFP_NOIO in the transmit code.
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