Date:	Tue, 30 Sep 2008 17:40:54 -0700
From:	Andreas Dilger <adilger@....com>
To:	Akira Fujita <a-fujita@...jp.nec.com>
Cc:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC][PATCH 0/12]ext4: online defrag (ver 0.95)

On Sep 27, 2008  16:26 +0900, Akira Fujita wrote:
> I've updated the ext4 online defragmentation patches.
> In this version, mainly there are following two changes and some fixes:
>   - Support 1KB and 2KB block size.
>   - Implement EXT4_IOC_FIEMAP_INO instead of EXT4_IOC_EXTENTS_INFO
>     to get extetns information.
> 
> Changelog:
> - 0.95(Sep. 26, 2008)
>   - Support 1KB and 2KB block size.
>   - Implement EXT4_IOC_FIEMAP_INO which calls ext4_fiemap() for specified inode number

Instead of implementing an EXT4_IOC_FIEMAP_INO ioctl, what we had implemented
is an EXT4_IOC_WRAPPER, which takes as arguments the inode number and the
ioctl command + original ioctl data.  This allows inode ioctls to be called
against the filesystem root for arbitrary inodes, and doesn't require new
implementation for each ioctl:

struct ll_ioctl_wrapper {
	__u32 ioctl_cmd;
	__u32 padding;
	__u64 ioctl_ino;
	char ioctl_data[0];
};

int ext4_ioctl(struct inode *inode, struct file *filp, unsigned int cmd,
	       unsigned long arg)
:
:
	case EXT4_IOC_WRAPPER: {
		struct inode *active_inode;
		struct ll_ioctl_wrapper buf;
		struct file_operations *fop;

		if (!capable(CAP_SYS_ADMIN))
			return -EACCES;

		if (copy_from_user(&buf, (struct ll_ioctl_wrapper __user *)arg,
				   sizeof(buf)))
			return -EFAULT;

		if (buf.ioctl_cmd == EXT4_IOC_WRAPPER)
			return -EDEADLK;

		active_inode = iget(lfs_sb, buf.ioctl_ino);
		if (!active_inode)
			return -EACCES;

		err = -ENOTTY;
		fop = inode->i_sb->s_root->d_inode->i_fop;
		if (fop && fop->unlocked_ioctl)
			err = fop->unlocked_ioctl(NULL, buf.ioctl_cmd,
						  arg + sizeof(buf));
		if ((!err || err != -ENOTTY))
			goto out_dput;

		if (fop && fop->ioctl)
			err = fop->ioctl(NULL, buf.ioctl_cmd, arg +sizeof(buf));
out_dput:
		iput(active_dentry);
		return err;
	}

>     instead of EXT4_IOC_EXTENTS_INFO to get extents information.
>   - Merge "JC6-defrag-alloc-contiguous-blks-credit" and
>     "ext4-request-for-blocks-with-ar.excepted_group-1.patch" in the ext4 patch queue
>     into this version.
>   - Handle s_dirtyblocks_counter correctly in defrag when delalloc enabled.
>   - Remove unneeded copy_from_user() in EXT4_IOC_GROUP_INFO ioctl.  Ted pointed this out.
> - 0.9 (May 30, 2008)
>   - Create some new functions (ext4_defrag_fill_ar(),
>     ext4_defrag_check_phase() ...) to separate block allocation function,
>     since the phase mode plug into the allocation function isn't good.
>   - Add the description of ext4_defrag() which is main function.
>   - Add the capability check.
>   - Some cleanups.
> - 0.8 (Apr. 8, 2008)
>     Fix sparse warnings and change the construction of patches.
> 
> Outline for ext4 online defragmentation:
> Ext4 online defrag has the following three functions.
> 
>  no option  Solving a single file fragmentation.
>	     Single file fragmentation is solved by moving file
>	     data to contiguous free blocks.
> 
>     -r      Solving a relevant file fragmentation.
>	     Relevant file fragmentation could be solved by moving
>	     the files under the specified directory close together with
>	     the block containing the directory data.
> 
>     -f      Solving a free space fragmentation.
>	     If there is no contiguous free blocks in the filesystem,
>	     the other files are moved to make sufficient space to allocate
>	     contiguous blocks for the target file.
> 
> Notes:
> - Ext4 online defarg needs "mballoc" and "extents" mount options.
> - "ext4-fiemap.patch" in the ext4 patch queue is necessary
>    for EXT4_IOC_FIEMAP_INO ioctl.  We have to apply fiemap patches previously
>    then apply defrag patches, so it is necessary to change
>    the order of series in the ext4 patch queue.
> 
> Next steps:
> 1. Address the following items that Ted pointed out.
>  - Move all of the defrag ioctls from ext4_defrag_ioctl() to ext4_ioctl()
>    so that defrag does not have a double layer ioctl's dispatch.
>  - Remove the block reservation in the force defrag (-f).
>  - Remove the EXT4_IOC_FIBMAP ioctl and use the EXT4_IOC_FIEMAP instead.
>  - Get super block information with opening block device in user space
>    so that we can remove the EXT4_IOC_GROUP_INFO ioctl.
> 
> Summary of patches:
> * The followings are new ext4 online defrag patches and they consist
>   of ioctl unit except 1-4.  Because the EXT4_IOC_DEFRAG is too big to review,
>   I divided it into 4 patches.
> 
> [PATCH 1/12] EXT4_IOC_DEFRAG ioctl and main functions of defrag
> - Create the temporary inode and do defrag per
>   defrag_size (defalut 64MB).
> 
> [PATCH 2/12] Allocate new contiguous blocks with mballoc
> - Search contiguous free blocks with mutil-block allocation
>   and allocate them for the temporary inode.
> 
> [PATCH 3/12] Read and write file data with memory page
> - Read the file data from the old blocks to the page cache and
>   write the file data on the page into the new blocks.
> 
> [PATCH 4/12]  Exchange the blocks between two inodes
> - Exchange the data blocks between the temporary inode and
>   the original inode.
> 
> [PATCH 5/12] EXT4_IOC_FIBMAP ioctl
> - The EXT4_IOC_FIBMAP ioctl gets the physical block offset of target inode
>   with ext4_bmap().  This ioctl is used only in the relevant defrag (-r).
> 
> [PATCH 6/12] EXT4_IOC_GROUP_INFO ioctl
> - The EXT4_IOC_GROUP_INFO ioctl gets the block group information
>   of target inode is located in.  This ioctl is used only in the force defrag (-f).
> 
> [PATCH 7/12] EXT4_IOC_FREE_BLOCKS_INFO ioctl
> - The EXT4_IOC_FREE_BLOCKS_INFO ioctl gets free extents
>   information of the target block group.
>   This ioctl is used only in the force defrag (-f).
> 
> [PATCH 8/12] EXT4_IOC_FIEMAP_INO ioctl
> - The EXT4_IOC_FIEMAP_INO is used to get extents information of
>   inode which set to ioctl.
>   The defragger uses this ioctl to check the fragment condition
>   and to get extents information in the specified block group.
> 
> [PATCH 9/12] EXT4_IOC_RESERVE_BLOCK ioctl
> - The EXT4_IOC_RESERVE_BLOCK ioctl reserves the specified
>   contiguous free space with ext4 block reservation function.
>   This ioctl is used only in the force defrag (-f).
> 
> [PATCH 10/12] EXT4_IOC_MOVE_VICTIM ioctl
> - The EXT4_IOC_MOVE_VICTIM moves the victim extents into other block group.
>   Therefore the contiguous free space is made in the target block group.
>   This ioctl is used only in the force defrag (-f).
> 
> [PATCH 11/12] EXT4_IOC_BLOCK_RELEASE ioctl
> - The EXT4_IOC_BLOCK_RELEASE releases the reserved blocks
>   which target inode holds.
>   This ioctl is used if defrag failed and it was after the block reservation.
> 
> [PATCH 12/12] Online defrag command
> - The defrag command. Usage is as follows:
>   - Defrag for a single file.
>     # e4defrag file-name
>   - Defrag for all files on ext4.
>     # e4defrag device-name
>   - Put the multiple files closer together.
>     # e4defrag -r directory-name
>   - Defrag for free space fragmentation.
>     # e4defrag -f file-name
> 
> Any comments and tests are welcome.
> 
> Best regards,
> Akira Fujita
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Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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