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SubjectRe: [PATCH 20/20] iscsi: support for swapping over iSCSI.
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On Wed, 2006-09-13 at 15:50 -0500, Mike Christie wrote:
> Peter Zijlstra wrote:
> > Implement sht->swapdev() for iSCSI. This method takes care of reserving
> > the extra memory needed and marking all relevant sockets with SOCK_VMIO.
> >
> > When used for swapping, TCP socket creation is done under GFP_MEMALLOC and
> > the TCP connect is done with SOCK_VMIO to ensure their success. Also the
> > netlink userspace interface is marked SOCK_VMIO, this will ensure that even
> > under pressure we can still communicate with the daemon (which runs as
> > mlockall() and needs no additional memory to operate).
> >
> > Netlink requests are handled under the new PF_MEM_NOWAIT when a swapper is
> > present. This ensures that the netlink socket will not block. User-space will
> > need to retry failed requests.
> >
> > The TCP receive path is handled under PF_MEMALLOC for SOCK_VMIO sockets.
> > This makes sure we do not block the critical socket, and that we do not
> > fail to process incomming data.
> >
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > CC: Mike Christie <michaelc@cs.wisc.edu>
> > ---
> > drivers/scsi/iscsi_tcp.c | 103 +++++++++++++++++++++++++++++++-----
> > drivers/scsi/scsi_transport_iscsi.c | 23 +++++++-
> > include/scsi/libiscsi.h | 1
> > include/scsi/scsi_transport_iscsi.h | 2
> > 4 files changed, 113 insertions(+), 16 deletions(-)
> >
> > Index: linux-2.6/drivers/scsi/iscsi_tcp.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/scsi/iscsi_tcp.c
> > +++ linux-2.6/drivers/scsi/iscsi_tcp.c
> > @@ -42,6 +42,7 @@
> > #include <scsi/scsi_host.h>
> > #include <scsi/scsi.h>
> > #include <scsi/scsi_transport_iscsi.h>
> > +#include <scsi/scsi_device.h>
> >
> > #include "iscsi_tcp.h"
> >
> > @@ -845,9 +846,13 @@ iscsi_tcp_data_recv(read_descriptor_t *r
> > int rc;
> > struct iscsi_conn *conn = rd_desc->arg.data;
> > struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
> > - int processed;
> > + int processed = 0;
> > char pad[ISCSI_PAD_LEN];
> > struct scatterlist sg;
> > + unsigned long pflags = current->flags;
> > +
> > + if (sk_has_vmio(tcp_conn->sock->sk))
> > + current->flags |= PF_MEMALLOC;
> >
>
> Is this too late or not needed or what is it for? This function gets run
> from the network layer's softirq and at this point we have a skbuff with
> data that we want to process. The iscsi layer also does not allocate
> memory for read or write IO in this path.

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);

> I think we would want to set this flag at a lower level. Something
> closer to where the skbuf is allocated?

Is that the skbuff you were talking about? If so, I'd need to carve a
path to pass the swapper information. I had that in a previous patch,
but that was large and ugly. I had to go carrying gfp_t flags all
through that call chain.

I could try again if you prefer that.

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