测试代码出自：块设备IO优化的典型案例分析_papaofdoudou的博客-CSDN博客_kworker/u2:2-2-

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
 
//O_DIRECT        
#define __USE_GNU 1
#include <fcntl.h>
#include <stdint.h>
#include <sys/mman.h>
#include <errno.h>
 
int fallocate(int , int , off_t, off_t);
static void write_test(int fdno)
{
	int origin_len;
	int reallen;
	void *mp;
 
	int len = 1 * 1024 * 1024;
	origin_len = len;
 
	len = len + (getpagesize() - len%getpagesize());
	//printf("%s line %d, len = %d.\n", __func__, __LINE__, len);
 
	unsigned char *p = malloc(len + getpagesize());
	if(p == NULL)
	{
		printf("%s line %d, malloc failure.\n", __func__, __LINE__);
		return;
	}
	mp = p;
 
	unsigned char *q = (unsigned char *)(((unsigned long)p + getpagesize())&(~(getpagesize()-1)));
	p = q;
 
	//printf("q = %p, mp = %p.\n", q, mp);
 
	memset(p, 0x00, len);
	//lseek(fdno, 0, SEEK_SET);
	//int reallen = read(fdno, p,len);
	//printf("%s line %d, reallen %d read failure.er %s\n", __func__, __LINE__, reallen, strerror(errno));
	//printf("%s line %d, fdno = %d\n", __func__, __LINE__, fdno);
	//lseek(fdno, 0, SEEK_SET);
 
	reallen = write(fdno, p, origin_len);
	//printf("%s line %d, reallen = %d.\n", __func__, __LINE__, reallen);
 
	//lseek(fdno, 0, SEEK_SET);
 
	free(mp);
	mp = NULL;
	return;
}
 
static void* write_thread1(void *p)
{
	int fdno;
 
	fdno = open("./fuck.bin", O_DIRECT|O_RDWR|O_CREAT, 0666);
	//fdno = open("./fuck.bin", O_RDWR|O_CREAT, 0666);
	if(fdno < 0)
	{
		printf("%s line %d, open file failure.\n", __func__, __LINE__);
		return NULL;
	}
 
	fallocate(fdno, 1, 0, 100*1024*1024);
	//fallocate(fdno, 0, 0, 100*1024*1024);
 
	//return NULL;
	while(1)
	{
		write_test(fdno);
	}
 
	close(fdno);
	return NULL;
}
 
static void* write_thread2(void *p)
{
	int fdno;
 
	fdno = open("./new.bin", O_DIRECT|O_RDWR|O_CREAT, 0666);
	if(fdno < 0)
	{
		printf("%s line %d, open file failure.\n", __func__, __LINE__);
		return NULL;
	}
 
	fallocate(fdno, 1, 0, 100*1024*1024);
	//fallocate(fdno, 0, 0, 100*1024*1024);
 
	//return NULL;
	while(1)
	{
		write_test(fdno);
	}
 
	close(fdno);
	return NULL;
}
 
int main(int argc,char **argv)
{
	pthread_t t1,t2;
 
	pthread_create(&t1,0,write_thread1,NULL);
	pthread_create(&t2,0,write_thread2,NULL);
 
	pthread_join(t1,NULL);
	pthread_join(t2,NULL);
 
	return 0;
}

块起始分别为9961472、9961984、9962496、9963008，每个需要512 sectiors 扇区，本次写1M的文件，需要4*512=1024个扇区，即每个扇区是1K

[281277.215000] test_emmc(14438): dirtied inode 1572868 (fuck.bin) on mmcblk0
[281277.215000] test_emmc(14438): WRITE block 9961472 on mmcblk0 (512 sectors)
[281277.215000] test_emmc(14438): WRITE block 9961984 on mmcblk0 (512 sectors)
[281277.219000] test_emmc(14438): WRITE block 9962496 on mmcblk0 (512 sectors)
[281277.220000] test_emmc(14438): WRITE block 9963008 on mmcblk0 (512 sectors)
[281283.008000] jbd2/mmcblk0-8(833): WRITE block 29730136 on mmcblk0 (8 sectors)
[281283.008000] jbd2/mmcblk0-8(833): WRITE block 29730144 on mmcblk0 (8 sectors)
[281283.013000] jbd2/mmcblk0-8(833): WRITE block 29730152 on mmcblk0 (8 sectors)
[281284.018000] kworker/u2:0(14315): WRITE block 50331904 on mmcblk0 (8 sectors)

问题1：jbd2/mmcblk0-8和kworker/u2:0有什么差别？

kworker线程创建

路径：kernel\workqueue.c

 

JBD2(journaling block device 2)

关于JBD介绍：https://help.aliyun.com/document_detail/155605.html

JDB的工作原理

JBD2(journaling block device 2)系统分析（一）-dessasic-ChinaUnix博客

性能分析之解决 jbd2 引起 IO 高问题_zuozewei的博客-CSDN博客

JDB2线程创建

[root@szclou mmcblk0-8]$ps -aux | grep jbd*
root       833  0.0  0.0      0     0 ?        S    Jan04   0:06 [jbd2/mmcblk0-8]
root     14546  0.0  0.3   1860   876 pts/2    S+   14:49   0:00 grep jbd*

JBD2源代码路径：fs\jbd2\journal.c

某大神发现jbd2日志更新时会引发io访问100%，是内核代码有bug，链接：性能分析之解决 jbd2 引起 IO 高问题_zuozewei的博客-CSDN博客

 而本人的内核却是还存在这个bug

int jbd2_log_start_commit(journal_t *journal, tid_t tid)
{
	int ret;

	write_lock(&journal->j_state_lock);
	ret = __jbd2_log_start_commit(journal, tid);
	write_unlock(&journal->j_state_lock);
	return ret;
}