Re:[RFC][PATCH 0/3] Extent base online defrag

Re:[RFC][PATCH 0/3] Extent base online defrag

[sho]

Hi,

Thank you for your trial and report of the result!

> Hi,
> I tried to use defrag utility. But these are the results that, I got:
> 
> [root@metis e4defrag]# ./defrag /dev/hda8
> Start defragment for device(/dev/hda8)
>        Total:                   393
>        Success:                   0 
>        Failure:                 393
> [root@metis e4defrag]# ./defrag /mnt/test1/root
> Start defragment for directory(/mnt/test1/root)
>        Total:                   392
>        Success:                   0
>        Failure:                 392
> I tried same thing with different directories and files, but the result
> was the same.
> By doing strace on defrag utility I found that ioctl always returned
> ENOSPC. So I decreased the no. files, but still that didn't help, I came
> down till filesystem was only 9% full.

I think that your files didn't have many fragments, so ioctl returned
ENOSPC.  e4defrag iterates ioctl per 64MB.  If the specified 64MB
range has only one fragment(extent), the kernel returns ENOSPC
at the current implement.
So I'll change this behaviour to realize whether there was actual
error.  I intend to update my patches in early December.

If you need to check the number of fragments(extents),
you can use the following simple program using Alex's debug code.
Example:
# ./scan_ext -e data0
Extents of data0:
start = 10240 len = 1024 block = 0
start = 212992 len = 1536 block = 1024
start = 197632 len = 1024 block = 2560
start = 450560 len = 1536 block = 3584
start = 662019 len = 1535 block = 5120
start = 721424 len = 1 block = 6655
start = 722944 len = 1024 block = 6656
start = 726016 len = 512 block = 7680

start: The physical block number.
len: The length of the extent.
block: The logical block number.

The program is following.
-----
#include <stdio.h>
#include <sys/ioctl.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


#define GET_EXTENTS	0
#define GET_STATUS	1
#define	GET_DEPTH	2

#define EXT3_IOC_GET_EXTENTS		_IOR('f', 7, long)
#define EXT3_IOC_GET_TREE_DEPTH		_IOR('f', 8, long)
#define EXT3_IOC_GET_TREE_STATS		_IOR('f', 9, long)

#define	BUF_LEN	1024

/*
 * this structure is used to gather extents from the tree via ioctl
 */
struct ext3_extent_buf {
	unsigned long start;
	int buflen;
	void *buffer;
	void *cur;
	int err;
};

/*
 * storage for cached extent
 */
struct ext3_ext_cache {
	unsigned int   ec_start;
	unsigned int   ec_block;
	unsigned int   ec_len;
	unsigned int   ec_type;
}; 

/*
 * this structure is used to collect stats info about the tree
 */
struct ext3_extent_tree_stats {
	int depth;
	int extents_num;
	int leaf_num;
};

struct ext3_ext_cache ec[BUF_LEN];

int
main(int argc, char **argv) {

	int cmd = EXT3_IOC_GET_EXTENTS;
	char	*file;
	int	fd;
	struct	ext3_extent_buf ebuf;
	void	*arg;
	struct ext3_extent_tree_stats	estat;
	int	ret;
	int	i;

	if (argc < 3) {
		fprintf(stderr, "Usage: scan_ext -e|-s|-d file\n");
		exit(1);
	}	

	if (!strcmp(argv[1], "-e")) {
		file = argv[2];
	} else if (!strcmp(argv[1], "-d")) {
		file = argv[2];
		cmd = EXT3_IOC_GET_TREE_DEPTH;	
	} else if (!strcmp(argv[1], "-s")) {
		file = argv[2];
		cmd = EXT3_IOC_GET_TREE_STATS;
	} else {
		file = argv[1];
	}

	if ((fd = open(file, O_RDONLY)) < 0) {
		perror("open");
		exit(1);
	}
		
	switch (cmd) {
	case EXT3_IOC_GET_EXTENTS:
		printf("Extents of %s:\n", argv[2]);
		ebuf.start = 0;
		ebuf.buflen = BUF_LEN * sizeof(struct ext3_ext_cache);
		ebuf.buffer = ebuf.cur = ec;
		ebuf.err = 0;
		arg = &ebuf;	
		break;
	case EXT3_IOC_GET_TREE_DEPTH:
		arg = NULL;	
		break;
	case EXT3_IOC_GET_TREE_STATS:
		arg = &estat;
		break;
	}

	if ((ret = ioctl(fd, cmd, arg)) < 0) {
		perror("ioctl");
		exit(1);
	}

	switch (cmd) {
	case EXT3_IOC_GET_EXTENTS:
		for(i = 0; i < ret; i++) {
			printf("start = %u len = %u block = %u\n",
				ec[i].ec_start, ec[i].ec_len,
				ec[i].ec_block); 
		}	
		break;
	case EXT3_IOC_GET_TREE_DEPTH:
		printf("depth = %d\n", ret);
		break;
	case EXT3_IOC_GET_TREE_STATS:
		printf("depth       = %d\n", estat.depth);
		printf("extents     = %d\n", estat.extents_num);
		printf("leaf blocks = %d\n", estat.leaf_num);
		break;
	}

	exit(0);
}

Cheers, Takashi

Re: Re:[RFC][PATCH 0/3] Extent base online defrag

[Girish Shilamkar]

Hello,


On Wed, 2006-11-29 at 23:39 +0900, sho@tnes.nec.co.jp wrote:
> Hi,
> 
> Thank you for your trial and report of the result!
> 
> > Hi,
> > I tried to use defrag utility. But these are the results that, I got:
> > 
> > [root@metis e4defrag]# ./defrag /dev/hda8
> > Start defragment for device(/dev/hda8)
> >        Total:                   393
> >        Success:                   0 
> >        Failure:                 393
> > [root@metis e4defrag]# ./defrag /mnt/test1/root
> > Start defragment for directory(/mnt/test1/root)
> >        Total:                   392
> >        Success:                   0
> >        Failure:                 39
> > I tried same thing with different directories and files, but the result
> > was the same.
> > By doing strace on defrag utility I found that ioctl always retunarned
> > ENOSPC. So I decreased the no. files, but still that didn't help, I came
> > down till filesystem was only 9% full.
> 
> I think that your files didn't have many fragments, so ioctl returned
> ENOSPC.  e4defrag iterates ioctl per 64MB.  If the specified 64MB
> range has only one fragment(extent), the kernel returns ENOSPC
> at the current implement.
> So I'll change this behaviour to realize whether there was actual
> error.  I intend to update my patches in early December.
> 
Thanks for responding and for the scan_ext3 program.
I did further testing, i checked if the file is fragmented or not :

[root@metis e4defrag]# ./scan_ext3 /mnt/test2/root/file3
Extents of /mnt/test2/root/file3:
start = 117919 len = 11316 block = 0
start = 136356 len = 2 block = 11316
start = 165920 len = 24 block = 11318
start = 165913 len = 7 block = 11342
start = 221200 len = 48 block = 11349
start = 221282 len = 1 block = 11397
start = 221295 len = 12 block = 11398
start = 221328 len = 1 block = 11410
start = 221381 len = 3 block = 11411
start = 221496 len = 1 block = 11414
start = 221517 len = 57 block = 11415
start = 221585 len = 53 block = 11472
start = 221673 len = 6 block = 11525 
start = 221681 len = 4 block = 11531
start = 221707 len = 1 block = 11535
start = 221711 len = 5 block = 11536
start = 221725 len = 25 block = 11541

>From the test the file seems to be pretty fragmented, still the defrag
utility gives ENOSPC error.

[root@metis e4defrag]# strace -e
trace=ioctl ./defrag /mnt/test2/root/file3
Start defragment for /mnt/test2/root/file3
ioctl(3, 0x4010660a, 0xbf8747c0)        = -1 ENOSPC (No space left on
device) 
        e4defrag  : defrag fail.: No space left on device
                    "/mnt/test2/root/file3"
[root@metis ~]# ll -h /mnt/test2/root/file3
-rw-r--r--  1 root root 159M Sep  2 10:34 /mnt/test2/root/file3

Most probably Rupesh(cc'ed him) will be looking into it further, really
appreciate if you can add something to it.

Thanks & Regards,
Girish.

Re:[RFC][PATCH 0/3] Extent base online defrag

[sho]

Hi,

Thank you for your further testing.

>From the test the file seems to be pretty fragmented, still the defrag
>utility gives ENOSPC error.

I found the problem of the workaround code related to journal in my
patches.  2048 blocks was always passed to ext3_journal_start so that
the journal blocks in transaction didn't exceed j_max_transaction_buffers.
However, j_max_transaction_buffers could be adjusted to the number of
filesystem blocks.  Maybe your filesystem's j_max_transaction_buffers
would be less than 2048, so the error would occur.

When the above problem occurs, the following message will be output
in syslog.  Could you check your syslog?

"JBD: e4defrag wants too many credits (2048 > XXXX)"

I am working for fixing the workaround code, but the work isn't
finished yet.  I will update my patches next week.
If you need to run my defrag soon, you can use the following
patch to avoid the above problem as the provisional solution.

After Alex's patches and my previous patches are applied,
you can apply the following patch.
---
diff -uprN -X linux-2.6.16.8-tnes-org/Documentation/dontdiff linux-2.6.16.8-tnes-org/fs/ext3/extents.c linux-2.6.16.8-work/fs/ext3/extents.c
--- linux-2.6.16.8-tnes-org/fs/ext3/extents.c	2006-12-01 10:37:28.000000000 +0900
+++ linux-2.6.16.8-work/fs/ext3/extents.c	2006-12-01 17:23:38.000000000 +0900
@@ -2738,6 +2738,7 @@ ext3_ext_replace_branches(struct ext3_ex
 	handle_t *handle = NULL;
 	unsigned jnum;
 	struct inode *inode;
+	journal_t	*journal;
 
 
 	from = from_page << (PAGE_CACHE_SHIFT - dest_tree->inode->i_blkbits);
@@ -2752,10 +2753,11 @@ ext3_ext_replace_branches(struct ext3_ex
 	 */
 	/* TODO:
 	 * Need to consider the way of calculating journal blocks
-	 * because j_max_transaction_buffer may exceed 2048
+	 * because the journal blocks may exceed j_max_transaction_buffer
 	 * if we have a deep depth.
 	 */
-	jnum = 2048;
+	journal = EXT3_JOURNAL(inode);
+	jnum = journal->j_max_transaction_buffers;
 	handle = ext3_journal_start(inode, jnum);
 	if (IS_ERR(handle)) {
 		err = PTR_ERR(handle);
@@ -3093,6 +3095,7 @@ ext3_ext_new_extent_tree(struct inode *t
 	unsigned jnum;
 	int ret = 0, err = 0, depth;
 	int last_extent = 0;
+	journal_t	*journal;
 
 	/* (blocks_per_page * count) * (extent_blocks + index_blocks)
 	 * + super_block + block_bitmap + group_descriptor
@@ -3100,10 +3103,11 @@ ext3_ext_new_extent_tree(struct inode *t
 	 */
 	/* TODO:
 	 * Need to consider the way of calculating journal blocks
-	 * because j_max_transaction_buffer may exceed 2048
+	 * because the journal blocks may exceed j_max_transaction_buffer
 	 * if we have a deep depth.
 	 */
-	jnum = 2048;
+	journal = EXT3_JOURNAL(tmp_inode);
+	jnum = journal->j_max_transaction_buffers; 
 	eh = EXT_ROOT_HDR(dest_tree);
 	eh->eh_depth = 0;
 	handle = ext3_journal_start(tmp_inode, jnum);

Cheers, Takashi