[PATCH wq/for-3.14 1/2] workqueue: update max_active clamping rules

Tejun Heo
2013-12-19T23:35:32Z

>From bdd220b2a1b86fee14a12b69fb0cadafe60a1dac Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Thu, 19 Dec 2013 18:33:09 -0500

@max_active handling is currently inconsistent.

* In alloc_workqueue(), 0 gets converted to the default and the value
gets clamped to [1, lim].

* In workqueue_set_max_active(), 0 is not converted to the default and
the value is clamped to [1, lim].

* When a workqueue is exposed through sysfs, input < 1 fails with
-EINVAL; otherwise, the value is clamped to [1, lim].

* fscache exposes max_active through a sysctl and clamps the value in
[1, lim].

We want to be able to express zero @max_active but as it's a special
case and 0 is already used for default, don't want to use 0 for it.
Update @max_active clamping so that the following rules are followed.

* In both alloc_workqueue() and workqueue_set_max_active(), 0 is
converted to the default, and a new special value WQ_FROZEN_ACTIVE
becomes 0; otherwise, the value is clamped to [1, lim].

* In both sysfs and fscache sysctl, input < 1 fails with -EINVAL;
otherwise, the value is clamped to [1, lim].

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: David Howells <dhowells@redhat.com>
---
fs/fscache/main.c | 10 +++++++---
include/linux/workqueue.h | 1 +
kernel/workqueue.c | 6 +++++-
3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index 7c27907..9d5a716 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -62,9 +62,13 @@ static int fscache_max_active_sysctl(struct ctl_table *table, int write,
int ret;

ret = proc_dointvec(table, write, buffer, lenp, ppos);
- if (ret == 0)
- workqueue_set_max_active(*wqp, *datap);
- return ret;
+ if (ret < 0)
+ return ret;
+ if (*datap < 1)
+ return -EINVAL;
+
+ workqueue_set_max_active(*wqp, *datap);
+ return 0;
}

ctl_table fscache_sysctls[] = {
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 594521b..334daa3 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -338,6 +338,7 @@ enum {
__WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
__WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */

+ WQ_FROZEN_ACTIVE = -1, /* special value for frozen wq */
WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
WQ_DFL_ACTIVE = WQ_MAX_ACTIVE / 2,
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 987293d..6748fbf 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4136,6 +4136,11 @@ static int wq_clamp_max_active(int max_active, unsigned int flags,
{
int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;

+ if (max_active == 0)
+ return WQ_DFL_ACTIVE;
+ if (max_active == WQ_FROZEN_ACTIVE)
+ return 0;
+
if (max_active < 1 || max_active > lim)
pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
max_active, name, 1, lim);
@@ -4176,7 +4181,6 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
vsnprintf(wq->name, sizeof(wq->name), fmt, args);
va_end(args);

- max_active = max_active ?: WQ_DFL_ACTIVE;
max_active = wq_clamp_max_active(max_active, flags, wq->name);

/* init wq */
--
1.8.4.2