Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait

Christoph Hellwig
2001-02-06T20:28:21Z

On Tue, Feb 06, 2001 at 11:32:43AM -0800, Linus Torvalds wrote:
> Traditionally, a "bh" is only _used_ for small areas, but that's not a
> "bh" issue, that's a memory management issue. The code should pretty much
> handle the issue of a single 64kB bh pretty much as-is, but nothing
> creates them: the VM layer only creates bh's in sizes ranging from 512
> bytes to a single page.
>
> The IO layer could do more, but there has yet to be anybody who needed
> more (becase once you hit a page-size, you tend to get into
> scatter-gather, so you want to have one bh per area - and let the
> low-level IO level handle the actual merging etc).

Yes. That's one disadvantage blown away.

The second is that bh's are two things:

- a cacheing object
- an io buffer

This is not really an clean appropeach, and I would really like to
get away from it.

Christoph

--
Whip me. Beat me. Make me maintain AIX.