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Revision c4f675cd40d955d539180506c09515c90169b15b authored by Sergei Trofimovich on 20 May 2011, 20:20:30 UTC, committed by Chris Mason on 23 May 2011, 17:24:14 UTC 
btrfs: don't spin in shrink_delalloc if there is nothing to free
 
Observed as a large delay when --mixed filesystem is filled up.
Test example:
1. create tiny --mixed FS:
   $ dd if=/dev/zero of=2G.img seek=$((2048 * 1024 * 1024 - 1)) count=1 bs=1
   $ mkfs.btrfs --mixed 2G.img
   $ mount -oloop 2G.img /mnt/ut/
2. Try to fill it up:
   $ dd if=/dev/urandom of=10M.file bs=10240 count=1024
   $ seq 1 256 | while read file_no; do echo $file_no; time cp 10M.file ${file_no}.copy; done

Up to '200.copy' it goes fast, but when disk fills-up each -ENOSPC
message takes 3 seconds to pop-up _every_ ENOSPC (and in usermode linux
it's even more: 30-60 seconds!). (Maybe, time depends on kernel's timer resolution).

No IO, no CPU load, just rescheduling. Some debugging revealed busy spinning
in shrink_delalloc.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Reviewed-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
1 parent 0f3b708
Raw File
cpu-notifier-error-inject.c 
#include <linux/kernel.h>
#include <linux/cpu.h>
#include <linux/module.h>
#include <linux/notifier.h>

static int priority;
static int cpu_up_prepare_error;
static int cpu_down_prepare_error;

module_param(priority, int, 0);
MODULE_PARM_DESC(priority, "specify cpu notifier priority");

module_param(cpu_up_prepare_error, int, 0644);
MODULE_PARM_DESC(cpu_up_prepare_error,
		"specify error code to inject CPU_UP_PREPARE action");

module_param(cpu_down_prepare_error, int, 0644);
MODULE_PARM_DESC(cpu_down_prepare_error,
		"specify error code to inject CPU_DOWN_PREPARE action");

static int err_inject_cpu_callback(struct notifier_block *nfb,
				unsigned long action, void *hcpu)
{
	int err = 0;

	switch (action) {
	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
		err = cpu_up_prepare_error;
		break;
	case CPU_DOWN_PREPARE:
	case CPU_DOWN_PREPARE_FROZEN:
		err = cpu_down_prepare_error;
		break;
	}
	if (err)
		printk(KERN_INFO "Injecting error (%d) at cpu notifier\n", err);

	return notifier_from_errno(err);
}

static struct notifier_block err_inject_cpu_notifier = {
	.notifier_call = err_inject_cpu_callback,
};

static int err_inject_init(void)
{
	err_inject_cpu_notifier.priority = priority;

	return register_hotcpu_notifier(&err_inject_cpu_notifier);
}

static void err_inject_exit(void)
{
	unregister_hotcpu_notifier(&err_inject_cpu_notifier);
}

module_init(err_inject_init);
module_exit(err_inject_exit);

MODULE_DESCRIPTION("CPU notifier error injection module");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Akinobu Mita <akinobu.mita@gmail.com>");
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