Re: [STATUS 2.5] May 1, 2002

From: Andrew Morton (
Date: Wed May 01 2002 - 16:38:37 EST

Mike Fedyk wrote:
> On Wed, May 01, 2002 at 09:53:37AM -0400, Guillaume Boissiere wrote:
> > new framebuffer layer, as well as some more delayed disk block
> > allocation bits.
> Actually Andrews work on address_space based writeback is related somewhat,
> but really it's a rewrite/cleanup of the buffer layer. Delayed block
> alocation is helped alot by this, and almost depends on it IIRC.
> One vote for a seperate listing in the status for "Address Space based
> Writeback / Buffer layer cleanup".

Well the next major step here is going direct
pagecache<->BIO, bypassing the intermediate submit_bh
for most I/O.

Probably that will make most of the performance benefits
of delayed-allocate go away.

There are other reasons for implementing delalloc
(XFS, improved layout, ...). So it ain't dead yet.

At 48 bytes, 2.5's buffer_head is now precisely half the
size of 2.4's. I'm hoping to be able to shed another eight
bytes yet.

With the pagecache<->BIO change, the buffer_head will most
definitely become "per-page metadata which describes the state
of sub-page segments" and not "something which is used for
performing I/O".

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