The first session of the summit was the requirements panel - a two hour
discussion on desired features in future versions of the Linux kernel. The
- Wim Coekaerts, Oracle kernel team.
- Walter Feldman, Unilever (which, he says, is moving large sections
of its global operations to Linux).
- Bdale Garbee, recently named HP's Linux Chief Technology
- Robert Lefkowitz from "Big Unnamed Financial Institution" (the company
did not want its name used at this event).
- Paul McKenney, IBM
- Tim Witham, Lab director, OSDL.
Each of the panelists was given an opportunity to present a wish list of
desired kernel features. There was, as it turns out, quite a bit of
overlap between their needs. Themes that came up include:
- Supporting large numbers of devices. At a minimum, 4,000 real
devices need to be supportable on 32-bit systems. Linus pointed out
that the x86 architecture is the real limiting factor; after a while,
there is simply not enough low memory to keep track of that many
devices. He is also not to thrilled by the recent 4G/4G patch
(covered in the July 17
LWN Kernel Page), calling it "tasteless." This patch does make it
possible to handle more devices (and memory), however, and Linus may
eventually be prepared to merge it as an option. The real solution,
though, is to
"get off the drugs" and go to 64-bit systems if you need that many
- There was also a request for support of truly large memory (up to
32GB) on 32-bit systems. That support is possible now - with the
- Run-time storage reconfiguration without downtime. Moving disks and
partitions around is a common operation, and they don't want to have
to take the systems down to do it.
- Proper multipath I/O support. This item also relates to the
"no downtime" requirement; the system needs to respond to I/O
subsystem failures without going down.
- Distributed filesystems. Commercial offerings exist, but
there is a real need for free, distributed filesystems. IBM has one
in the process of being released, but IBM's lawyers are "busy with
other tasks" at the moment. It was pointed out that Oracle has
released its cluster filesystem under the GPL. Also available is OpenAFS, though
its support in 2.6 is not what all would like. It was suggested that
better support in the generic filesystem levels for clustered
filesystems would be helpful.
- A cluster-aware logical volume manager is also on the list.
- A "more flexible" virtual memory subsystem. In particular, there is
a desire for better control over memory usage by processes and process
- The Big Unnamed Financial Institution representative spoke of a strong
need for virtual machine support. Many of BUFI's applications require
strict separation from each other; heavy use of virtual machines also
makes testing of upgrades easier. Robert predicted that, in the near
future, a substantial portion of deployed desktop Linux systems will
actually be running under a system like VMware. User-mode Linux also
works well for much of what BUFI is trying to do.
- Persistent device naming was mentioned by Bdale. When you have
thousands of devices to manage, it really doesn't work to have them
changing names frequently.
- Transparent superpages (support of large physical pages without the
need for application changes). Large page support is available now,
but it requires explicit calls from the application.
- Better support for performance counters. All of the existing
performance counter implementations are either specific to a
particular architecture, or to a specific application.
- Crash dump support. Vendors really do need this capability to
diagnose problems encountered by their customers.
- Interrupt balancing. The hooks need to be put into place to allow
user-space to query performance and set interrupt balancing policy.
- A process checkpoint and restart mechanism which eventually could
grow to support migration of processes across systems.
- Asynchronous I/O for network operations.
- Standardized error logging which makes more sense to machines
and humans alike. A more generalized, standard event reporting
mechanism was also requested.
Linus reacted all of the above by asking about the needs of people with
small systems - a group which makes up the majority of Linux users. Linux,
he said, will not take over the very large systems arena at the expense of
smaller systems. It was pointed out that many of the wishlist items are
useful for smaller systems as well; an error and event notification
mechanism can be used to inform the user of a low battery or full disk, for
The purpose of the session was to get the wishes out on the table, so few
conclusions were reached. Much of this list will be revisited, in more
detail, over the course of the summit.
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