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Date: Fri, 30 Jan 2009 15:15:18 -0500 From: Chris Mason <chris.mason@...cle.com> To: Akira Fujita <a-fujita@...jp.nec.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) On Fri, 2009-01-30 at 15:11 +0900, Akira Fujita 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. > One thing you'll want to handle is swap files. The swap code uses the bmap ioctl to make a mapping of extents in the files, and expects that mapping not to change. So, defragging a swap file will lead to some serious problems. Btrfs is currently getting around this by dropping bmap support, so swapfiles on btrfs won't work at all. A real long term solution is required ;) For ext4 you should be able to just detect swapfile and disallow the defrag on it. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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