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>
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@ -18,6 +18,7 @@
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#include <linux/writeback.h>
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#include <linux/writeback.h>
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#include <linux/atomic.h>
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#include <linux/atomic.h>
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#include <linux/sysctl.h>
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#include <linux/sysctl.h>
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#include <linux/mutex.h>
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struct page;
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struct page;
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struct device;
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struct device;
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@ -105,6 +106,9 @@ struct backing_dev_info {
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struct timer_list laptop_mode_wb_timer;
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struct timer_list laptop_mode_wb_timer;
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cpumask_t *flusher_cpumask; /* used for writeback thread scheduling */
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struct mutex flusher_cpumask_lock;
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#ifdef CONFIG_DEBUG_FS
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#ifdef CONFIG_DEBUG_FS
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struct dentry *debug_dir;
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struct dentry *debug_dir;
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struct dentry *debug_stats;
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struct dentry *debug_stats;
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@ -10,6 +10,7 @@
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#include <linux/module.h>
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#include <linux/module.h>
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#include <linux/writeback.h>
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#include <linux/writeback.h>
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#include <linux/device.h>
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#include <linux/device.h>
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#include <linux/slab.h>
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#include <trace/events/writeback.h>
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#include <trace/events/writeback.h>
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static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
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static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
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@ -221,12 +222,63 @@ static ssize_t max_ratio_store(struct device *dev,
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}
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}
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BDI_SHOW(max_ratio, bdi->max_ratio)
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BDI_SHOW(max_ratio, bdi->max_ratio)
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static ssize_t cpu_list_store(struct device *dev,
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struct device_attribute *attr, const char *buf, size_t count)
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{
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struct backing_dev_info *bdi = dev_get_drvdata(dev);
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struct bdi_writeback *wb = &bdi->wb;
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cpumask_var_t newmask;
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ssize_t ret;
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struct task_struct *task;
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if (!alloc_cpumask_var(&newmask, GFP_KERNEL))
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return -ENOMEM;
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ret = cpulist_parse(buf, newmask);
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if (!ret) {
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spin_lock_bh(&bdi->wb_lock);
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task = wb->task;
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if (task)
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get_task_struct(task);
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spin_unlock_bh(&bdi->wb_lock);
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mutex_lock(&bdi->flusher_cpumask_lock);
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if (task) {
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ret = set_cpus_allowed_ptr(task, newmask);
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put_task_struct(task);
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}
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if (ret == 0) {
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cpumask_copy(bdi->flusher_cpumask, newmask);
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ret = count;
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}
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mutex_unlock(&bdi->flusher_cpumask_lock);
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}
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free_cpumask_var(newmask);
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return ret;
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}
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static ssize_t cpu_list_show(struct device *dev,
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struct device_attribute *attr, char *page)
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{
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struct backing_dev_info *bdi = dev_get_drvdata(dev);
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ssize_t ret;
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mutex_lock(&bdi->flusher_cpumask_lock);
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ret = cpulist_scnprintf(page, PAGE_SIZE-1, bdi->flusher_cpumask);
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mutex_unlock(&bdi->flusher_cpumask_lock);
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return ret;
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}
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#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
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#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
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static struct device_attribute bdi_dev_attrs[] = {
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static struct device_attribute bdi_dev_attrs[] = {
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__ATTR_RW(read_ahead_kb),
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__ATTR_RW(read_ahead_kb),
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__ATTR_RW(min_ratio),
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__ATTR_RW(min_ratio),
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__ATTR_RW(max_ratio),
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__ATTR_RW(max_ratio),
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__ATTR_RW(cpu_list),
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__ATTR_NULL,
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__ATTR_NULL,
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};
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};
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@ -428,6 +480,7 @@ static int bdi_forker_thread(void *ptr)
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writeback_inodes_wb(&bdi->wb, 1024,
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writeback_inodes_wb(&bdi->wb, 1024,
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WB_REASON_FORKER_THREAD);
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WB_REASON_FORKER_THREAD);
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} else {
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} else {
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int ret;
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/*
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/*
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* The spinlock makes sure we do not lose
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* The spinlock makes sure we do not lose
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* wake-ups when racing with 'bdi_queue_work()'.
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* wake-ups when racing with 'bdi_queue_work()'.
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@ -437,6 +490,14 @@ static int bdi_forker_thread(void *ptr)
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spin_lock_bh(&bdi->wb_lock);
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spin_lock_bh(&bdi->wb_lock);
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bdi->wb.task = task;
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bdi->wb.task = task;
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spin_unlock_bh(&bdi->wb_lock);
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spin_unlock_bh(&bdi->wb_lock);
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mutex_lock(&bdi->flusher_cpumask_lock);
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ret = set_cpus_allowed_ptr(task,
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bdi->flusher_cpumask);
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mutex_unlock(&bdi->flusher_cpumask_lock);
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if (ret)
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printk_once("%s: failed to bind flusher"
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" thread %s, error %d\n",
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__func__, task->comm, ret);
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wake_up_process(task);
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wake_up_process(task);
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}
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}
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bdi_clear_pending(bdi);
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bdi_clear_pending(bdi);
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@ -509,6 +570,17 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
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dev_name(dev));
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dev_name(dev));
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if (IS_ERR(wb->task))
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if (IS_ERR(wb->task))
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return PTR_ERR(wb->task);
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return PTR_ERR(wb->task);
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} else {
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int node;
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/*
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* Set up a default cpumask for the flusher threads that
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* includes all cpus on the same numa node as the device.
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* The mask may be overridden via sysfs.
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*/
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node = dev_to_node(bdi->dev);
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if (node != NUMA_NO_NODE)
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cpumask_copy(bdi->flusher_cpumask,
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cpumask_of_node(node));
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}
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}
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bdi_debug_register(bdi, dev_name(dev));
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bdi_debug_register(bdi, dev_name(dev));
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@ -634,6 +706,15 @@ int bdi_init(struct backing_dev_info *bdi)
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bdi_wb_init(&bdi->wb, bdi);
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bdi_wb_init(&bdi->wb, bdi);
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if (!bdi_cap_flush_forker(bdi)) {
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bdi->flusher_cpumask = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
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if (!bdi->flusher_cpumask)
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return -ENOMEM;
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cpumask_setall(bdi->flusher_cpumask);
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mutex_init(&bdi->flusher_cpumask_lock);
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} else
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bdi->flusher_cpumask = NULL;
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for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
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for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
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err = percpu_counter_init(&bdi->bdi_stat[i], 0);
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err = percpu_counter_init(&bdi->bdi_stat[i], 0);
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if (err)
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if (err)
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@ -656,6 +737,7 @@ int bdi_init(struct backing_dev_info *bdi)
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err:
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err:
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while (i--)
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while (i--)
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percpu_counter_destroy(&bdi->bdi_stat[i]);
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percpu_counter_destroy(&bdi->bdi_stat[i]);
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kfree(bdi->flusher_cpumask);
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}
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}
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return err;
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return err;
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@ -683,6 +765,8 @@ void bdi_destroy(struct backing_dev_info *bdi)
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bdi_unregister(bdi);
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bdi_unregister(bdi);
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kfree(bdi->flusher_cpumask);
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/*
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/*
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* If bdi_unregister() had already been called earlier, the
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* If bdi_unregister() had already been called earlier, the
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* wakeup_timer could still be armed because bdi_prune_sb()
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* wakeup_timer could still be armed because bdi_prune_sb()
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