From ee04a8fbdfe558bd63cd5b0309f1387803d0e2f0 Mon Sep 17 00:00:00 2001
From: t_jeang <devnull@localhost>
Date: Tue, 6 Jan 2009 12:06:01 +0000
Subject: [PATCH] imported patch blktap-ioprio.patch

---
 include/linux/init_task.h |  1 +
 include/linux/resource.h  |  1 +
 include/linux/sched.h     |  1 +
 kernel/sys.c              | 18 ++++++++++++++----
 mm/page-writeback.c       |  3 +++
 5 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index b6ef1280..7277ebdf 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -89,6 +89,7 @@ extern struct group_info init_groups;
 	.lock_depth	= -1,						\
 	.prio		= MAX_PRIO-20,					\
 	.static_prio	= MAX_PRIO-20,					\
+	.special_prio	= 0,						\
 	.normal_prio	= MAX_PRIO-20,					\
 	.policy		= SCHED_NORMAL,					\
 	.cpus_allowed	= CPU_MASK_ALL,					\
diff --git a/include/linux/resource.h b/include/linux/resource.h
index 14757afe..eec6bd96 100644
--- a/include/linux/resource.h
+++ b/include/linux/resource.h
@@ -46,6 +46,7 @@ struct rlimit {
 
 #define	PRIO_MIN	(-20)
 #define	PRIO_MAX	20
+#define PRIO_SPECIAL_IO -9999
 
 #define	PRIO_PROCESS	0
 #define	PRIO_PGRP	1
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ee07ae3a..445b82e9 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -823,6 +823,7 @@ struct task_struct {
 	struct prio_array *array;
 
 	unsigned short ioprio;
+	short special_prio;
 	unsigned int btrace_seq;
 
 	unsigned long sleep_avg;
diff --git a/kernel/sys.c b/kernel/sys.c
index 7695fc56..25782410 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -444,6 +444,11 @@ static int set_one_prio(struct task_struct *p, int niceval, int error)
 		error = -EPERM;
 		goto out;
 	}
+	if (niceval == PRIO_SPECIAL_IO) {
+		p->special_prio = PRIO_SPECIAL_IO;
+		error = 0;
+		goto out;
+	}
 	if (niceval < task_nice(p) && !can_nice(p, niceval)) {
 		error = -EACCES;
 		goto out;
@@ -471,10 +476,15 @@ asmlinkage long sys_setpriority(int which, int who, int niceval)
 
 	/* normalize: avoid signed division (rounding problems) */
 	error = -ESRCH;
-	if (niceval < -20)
-		niceval = -20;
-	if (niceval > 19)
-		niceval = 19;
+	if (niceval == PRIO_SPECIAL_IO) {
+		if (which != PRIO_PROCESS)
+			return -EINVAL;
+	} else {
+		if (niceval < -20)
+			niceval = -20;
+		if (niceval > 19)
+			niceval = 19;
+	}
 
 	read_lock(&tasklist_lock);
 	switch (which) {
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index e9fb4024..c23c2558 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -220,6 +220,9 @@ static void balance_dirty_pages(struct address_space *mapping)
 			pages_written += write_chunk - wbc.nr_to_write;
 			if (pages_written >= write_chunk)
 				break;		/* We've done our duty */
+			if (current->special_prio == PRIO_SPECIAL_IO)
+				break;          /* Exempt IO processes */
+
 		}
 		blk_congestion_wait(WRITE, HZ/10);
 	}
-- 
2.39.5