linux-ext4 - Re: [RFC][PATCH 0/3] ext4: online defrag (ver 1.0)

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Date:	Wed, 04 Feb 2009 17:07:48 +0900
From:	Akira Fujita <a-fujita@...jp.nec.com>
To:	Greg Freemyer <greg.freemyer@...il.com>
CC:	Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC][PATCH 0/3] ext4: online defrag (ver 1.0)

Hi Greg,

Greg Freemyer wrote:
> On Fri, Jan 30, 2009 at 1:11 AM, Akira Fujita <a-fujita@...jp.nec.com> wrote:
>> Hi,
>>
>> I have rewritten ext4 online defrag patches based on the comments from Ted.
>> In the new defrag, create donor inode in the user space instead of kernel space,
>> and then allocate contiguous blocks to it with fallocate().
>> In kernel space, exchange the blocks between target inode and donor inode,
>> and then copy the file data of target inode to donor inode every 64MB.
>> The EXT4_IOC_DEFRAG ioctl becomes simpler than the old one,
>> so it may be useful for other purposes.
>>
>> #define EXT4_IOC_DEFRAG                 _IOW('f', 15, struct move_extent)
>>
> 

I see.  Does EXT4_IOC_MOVE_EXT sound better for you?

#define EXT4_IOC_MOVE_EXT             _IOW('f', 15, struct move_extent)

> Do we want the ioctl name to be specific to defrag?  I thought Ted's
> goal was to make it more generic?  I can also envision this same ioctl
> being implemented by other file systems so EXT4 seems an inappropriate
> prefix.

Other filesystems (e.g. xfs, btrfs) have their own defrag ioctl,
and ext2/3 can not use this ioctl because they do not handle
extent file, though.
What kind of advantage do you think by moving this ioctl
to vfs layer?


> Thoughts?
> 
>> struct move_extent {
>>        int org_fd;             /* original file descriptor */
>>        int dest_fd;            /* destination file descriptor */
>>        ext4_lblk_t start;      /* logical offset of org_fd and dest_fd */
>>        ext4_lblk_t len;        /* exchange block length */
>> };
> 
> I would also like to see .dest_fd changed to .donor_fd.
> 
> I would like to see the ABI be more flexible and have .start be broken
> into 2 fields:
> 
> .start_orig
> .start_donor
> 
> And I don't think they should be of type ext4_lblk_t.  Something more
> generic seems appropriate.
> 
OK, I broke .start into .orig_start and .donor_start
and changed the entry type from ext4_lblk_t to __u64.
The new move_extent structure is as follows:

struct move_extent {
          int orig_fd;            /* original file descriptor */
          int donor_fd;           /* donor file descriptor */
          __u64 orig_start;       /* logical start offset in block for orig */
          __u64 donor_start;      /* logical start offset in block for donor */
          __u64 len;              /* exchange block length */
};

Any comments?

Regards,
Akira Fujita
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