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SubjectRe: [PATCH 20/20] iscsi: support for swapping over iSCSI.
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 think we would want to set this flag at a lower level. Something
closer to where the skbuf is allocated?
-
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