linux-ext4 - Re: [RFC] System calls for online defrag

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Message-Id: <1189027907.13189.3.camel@eric-laptop>
Date:	Wed, 05 Sep 2007 14:31:47 -0700
From:	Eric <erpo41@...il.com>
To:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [RFC] System calls for online defrag

On Wed, 2007-09-05 at 16:24 +0200, Jan Kara wrote:
> On Tue 04-09-07 12:01:53, Andreas Dilger wrote:
> > On Sep 03, 2007  20:03 +0200, Jan Kara wrote:
> > >   I've finally got to writing up some proposal how could look system calls
> > > allowing for online filesystem defragmentation and generally moving file
> > > blocks around for improving performance. Comments are welcome.
> > > 
> > > int sys_movedata(int datafd, int spacefd, loff_t from, size_t len)
> > >    The call takes blocks used to carry data starting at offset @from of length
> > > @len in @spacefd and places them instead of corresponding blocks in @datafd.
> > 
> > Calling these "@spacefd" and "@datafd" is a bit confusing.  How about "@srcfd"
> > and "@tgtfd" instead?  For defragmentation, are you planning to have @datafd
> > be the "real" inode and "@spacefd" be the temporary inode with defragged data,
> > or the reverse?  It isn't really clear.
>   The idea behind the names was that you move data from @datafd into blocks
> provided by @spacefd. Calling it @srcfd and @tgtfd has the problem whether
> you mean source of data or source of blocks...

FWIW, I think @srcfd and @tgtfd are clearer.

When I think about changing the block on the disk that's associated with
a block's worth of data in a file, I think about scooping the file data
out of the source block and setting it down in the destination block. I
do not think about pulling the on-disk block out from under the data and
replacing it with a different on-disk block.

Cheers,

Eric

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