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    SubjectRe: [PATCH 00/17] Swap-over-NBD without deadlocking V10
    On 05/10/2012 08:44 AM, Mel Gorman wrote:
    > When a user or administrator requires swap for their application, they
    > create a swap partition and file, format it with mkswap and activate it
    > with swapon. Swap over the network is considered as an option in diskless
    > systems. The two likely scenarios are when blade servers are used as part
    > of a cluster where the form factor or maintenance costs do not allow the
    > use of disks and thin clients.

    Thank you for working on this. I made the attached patch for software
    iscsi which has the same issue as nbd.

    I tested the patch here and did not notice any performance regressions
    or any other bugs.
    From 917d53f16d1e26b12e90e5e15df76a7a8bee35e8 Mon Sep 17 00:00:00 2001
    From: Mike Christie <michaelc@cs.wisc.edu>
    Date: Thu, 3 May 2012 12:36:18 -0500
    Subject: [PATCH 1/1] iscsi: Set SOCK_MEMALLOC for access to PFMEMALLOC
    reserves

    Set SOCK_MEMALLOC on the iscsi socket to allow access to PFMEMALLOC
    reserves to prevent deadlock.

    Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
    ---
    drivers/scsi/iscsi_tcp.c | 18 +++++++++++++-----
    1 files changed, 13 insertions(+), 5 deletions(-)

    diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c
    index 453a740..7360f4c 100644
    --- a/drivers/scsi/iscsi_tcp.c
    +++ b/drivers/scsi/iscsi_tcp.c
    @@ -370,17 +370,24 @@ static inline int iscsi_sw_tcp_xmit_qlen(struct iscsi_conn *conn)
    static int iscsi_sw_tcp_pdu_xmit(struct iscsi_task *task)
    {
    struct iscsi_conn *conn = task->conn;
    - int rc;
    + unsigned long pflags = current->flags;
    + int rc = 0;
    +
    + current->flags |= PF_MEMALLOC;

    while (iscsi_sw_tcp_xmit_qlen(conn)) {
    rc = iscsi_sw_tcp_xmit(conn);
    - if (rc == 0)
    - return -EAGAIN;
    + if (rc == 0) {
    + rc = -EAGAIN;
    + break;
    + }
    if (rc < 0)
    - return rc;
    + break;
    + rc = 0;
    }

    - return 0;
    + tsk_restore_flags(current, pflags, PF_MEMALLOC);
    + return rc;
    }

    /*
    @@ -665,6 +672,7 @@ iscsi_sw_tcp_conn_bind(struct iscsi_cls_session *cls_session,
    sk->sk_reuse = 1;
    sk->sk_sndtimeo = 15 * HZ; /* FIXME: make it configurable */
    sk->sk_allocation = GFP_ATOMIC;
    + sk_set_memalloc(sk);

    iscsi_sw_tcp_conn_set_callbacks(conn);
    tcp_sw_conn->sendpage = tcp_sw_conn->sock->ops->sendpage;
    --
    1.7.7.6
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