netdev - [PATCH 12/14] nbd: Set SOCK_MEMALLOC for access to PFMEMALLOC reserves

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Date:	Mon, 20 Jun 2011 14:12:18 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>, Neil Brown <neilb@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>
Subject: [PATCH 12/14] nbd: Set SOCK_MEMALLOC for access to PFMEMALLOC reserves

Set SOCK_MEMALLOC on the NBD socket to allow access to PFMEMALLOC
reserves so pages backed by NBD, particularly if swap related,
can be cleaned to prevent the machine being deadlocked. It is
still possible that the PFMEMALLOC reserves get depleted resulting
in deadlock but this can be resolved by the administrator by
increasing min_free_kbytes.

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 drivers/block/nbd.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index f533f33..ca7cd81 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -156,6 +156,7 @@ static int sock_xmit(struct nbd_device *lo, int send, void *buf, int size,
 	struct msghdr msg;
 	struct kvec iov;
 	sigset_t blocked, oldset;
+	unsigned long pflags = current->flags;
 
 	if (unlikely(!sock)) {
 		printk(KERN_ERR "%s: Attempted %s on closed socket in sock_xmit\n",
@@ -168,8 +169,9 @@ static int sock_xmit(struct nbd_device *lo, int send, void *buf, int size,
 	siginitsetinv(&blocked, sigmask(SIGKILL));
 	sigprocmask(SIG_SETMASK, &blocked, &oldset);
 
+	current->flags |= PF_MEMALLOC;
 	do {
-		sock->sk->sk_allocation = GFP_NOIO;
+		sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
 		iov.iov_base = buf;
 		iov.iov_len = size;
 		msg.msg_name = NULL;
@@ -215,6 +217,7 @@ static int sock_xmit(struct nbd_device *lo, int send, void *buf, int size,
 	} while (size > 0);
 
 	sigprocmask(SIG_SETMASK, &oldset, NULL);
+	tsk_restore_flags(current, pflags, PF_MEMALLOC);
 
 	return result;
 }
@@ -405,6 +408,8 @@ static int nbd_do_it(struct nbd_device *lo)
 
 	BUG_ON(lo->magic != LO_MAGIC);
 
+	sk_set_memalloc(lo->sock->sk);
+
 	lo->pid = current->pid;
 	ret = sysfs_create_file(&disk_to_dev(lo->disk)->kobj, &pid_attr.attr);
 	if (ret) {
-- 
1.7.3.4

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