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bdi: add a user-tunable cpu_list for the bdi flusher threads

In realtime environments, it may be desirable to keep the per-bdi
flusher threads from running on certain cpus.  This patch adds a
cpu_list file to /sys/class/bdi/* to enable this.  The default is to tie
the flusher threads to the same numa node as the backing device (though
I could be convinced to make it a mask of all cpus to avoid a change in
behaviour).

Thanks to Jeremy Eder for the original idea.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
master
Jeff Moyer 10 years ago committed by Jens Axboe
parent
commit
8fa72d234d
  1. 4
      include/linux/backing-dev.h
  2. 84
      mm/backing-dev.c

4
include/linux/backing-dev.h

@ -18,6 +18,7 @@ @@ -18,6 +18,7 @@
#include <linux/writeback.h>
#include <linux/atomic.h>
#include <linux/sysctl.h>
#include <linux/mutex.h>
struct page;
struct device;
@ -105,6 +106,9 @@ struct backing_dev_info { @@ -105,6 +106,9 @@ struct backing_dev_info {
struct timer_list laptop_mode_wb_timer;
cpumask_t *flusher_cpumask; /* used for writeback thread scheduling */
struct mutex flusher_cpumask_lock;
#ifdef CONFIG_DEBUG_FS
struct dentry *debug_dir;
struct dentry *debug_stats;

84
mm/backing-dev.c

@ -10,6 +10,7 @@ @@ -10,6 +10,7 @@
#include <linux/module.h>
#include <linux/writeback.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <trace/events/writeback.h>
static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
@ -221,12 +222,63 @@ static ssize_t max_ratio_store(struct device *dev, @@ -221,12 +222,63 @@ static ssize_t max_ratio_store(struct device *dev,
}
BDI_SHOW(max_ratio, bdi->max_ratio)
static ssize_t cpu_list_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
struct backing_dev_info *bdi = dev_get_drvdata(dev);
struct bdi_writeback *wb = &bdi->wb;
cpumask_var_t newmask;
ssize_t ret;
struct task_struct *task;
if (!alloc_cpumask_var(&newmask, GFP_KERNEL))
return -ENOMEM;
ret = cpulist_parse(buf, newmask);
if (!ret) {
spin_lock_bh(&bdi->wb_lock);
task = wb->task;
if (task)
get_task_struct(task);
spin_unlock_bh(&bdi->wb_lock);
mutex_lock(&bdi->flusher_cpumask_lock);
if (task) {
ret = set_cpus_allowed_ptr(task, newmask);
put_task_struct(task);
}
if (ret == 0) {
cpumask_copy(bdi->flusher_cpumask, newmask);
ret = count;
}
mutex_unlock(&bdi->flusher_cpumask_lock);
}
free_cpumask_var(newmask);
return ret;
}
static ssize_t cpu_list_show(struct device *dev,
struct device_attribute *attr, char *page)
{
struct backing_dev_info *bdi = dev_get_drvdata(dev);
ssize_t ret;
mutex_lock(&bdi->flusher_cpumask_lock);
ret = cpulist_scnprintf(page, PAGE_SIZE-1, bdi->flusher_cpumask);
mutex_unlock(&bdi->flusher_cpumask_lock);
return ret;
}
#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
static struct device_attribute bdi_dev_attrs[] = {
__ATTR_RW(read_ahead_kb),
__ATTR_RW(min_ratio),
__ATTR_RW(max_ratio),
__ATTR_RW(cpu_list),
__ATTR_NULL,
};
@ -428,6 +480,7 @@ static int bdi_forker_thread(void *ptr) @@ -428,6 +480,7 @@ static int bdi_forker_thread(void *ptr)
writeback_inodes_wb(&bdi->wb, 1024,
WB_REASON_FORKER_THREAD);
} else {
int ret;
/*
* The spinlock makes sure we do not lose
* wake-ups when racing with 'bdi_queue_work()'.
@ -437,6 +490,14 @@ static int bdi_forker_thread(void *ptr) @@ -437,6 +490,14 @@ static int bdi_forker_thread(void *ptr)
spin_lock_bh(&bdi->wb_lock);
bdi->wb.task = task;
spin_unlock_bh(&bdi->wb_lock);
mutex_lock(&bdi->flusher_cpumask_lock);
ret = set_cpus_allowed_ptr(task,
bdi->flusher_cpumask);
mutex_unlock(&bdi->flusher_cpumask_lock);
if (ret)
printk_once("%s: failed to bind flusher"
" thread %s, error %d\n",
__func__, task->comm, ret);
wake_up_process(task);
}
bdi_clear_pending(bdi);
@ -509,6 +570,17 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent, @@ -509,6 +570,17 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
dev_name(dev));
if (IS_ERR(wb->task))
return PTR_ERR(wb->task);
} else {
int node;
/*
* Set up a default cpumask for the flusher threads that
* includes all cpus on the same numa node as the device.
* The mask may be overridden via sysfs.
*/
node = dev_to_node(bdi->dev);
if (node != NUMA_NO_NODE)
cpumask_copy(bdi->flusher_cpumask,
cpumask_of_node(node));
}
bdi_debug_register(bdi, dev_name(dev));
@ -634,6 +706,15 @@ int bdi_init(struct backing_dev_info *bdi) @@ -634,6 +706,15 @@ int bdi_init(struct backing_dev_info *bdi)
bdi_wb_init(&bdi->wb, bdi);
if (!bdi_cap_flush_forker(bdi)) {
bdi->flusher_cpumask = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
if (!bdi->flusher_cpumask)
return -ENOMEM;
cpumask_setall(bdi->flusher_cpumask);
mutex_init(&bdi->flusher_cpumask_lock);
} else
bdi->flusher_cpumask = NULL;
for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
err = percpu_counter_init(&bdi->bdi_stat[i], 0);
if (err)
@ -656,6 +737,7 @@ int bdi_init(struct backing_dev_info *bdi) @@ -656,6 +737,7 @@ int bdi_init(struct backing_dev_info *bdi)
err:
while (i--)
percpu_counter_destroy(&bdi->bdi_stat[i]);
kfree(bdi->flusher_cpumask);
}
return err;
@ -683,6 +765,8 @@ void bdi_destroy(struct backing_dev_info *bdi) @@ -683,6 +765,8 @@ void bdi_destroy(struct backing_dev_info *bdi)
bdi_unregister(bdi);
kfree(bdi->flusher_cpumask);
/*
* If bdi_unregister() had already been called earlier, the
* wakeup_timer could still be armed because bdi_prune_sb()

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