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SubjectRe: Please don't beat me up (was Re: Bugs and wishes in memory management area)
Date

In linux.dev.kernel, article <Pine.LNX.3.95.961127160222.2744A-100000@pc5829.hil.siemens.at>,
Ingo Molnar <mingo@pc5829.hil.siemens.at> writes:
>
> i dont get it [it must be me]. How would you allocate 2 consecutive pages
> in this 5-page pool which has 3 free pages? :
>
> page 1 -------> free
> page 2 -------> used by the Ethernet driver
> page 3 -------> free
> page 4 -------> used by the SCSI driver
> page 5 -------> free
>
You don't. But then you don't need to. The problem is that under the
current system, things like

page 0 -------> used by the Ethernet driver
page 1 -------> free
page 2 -------> free
page 3 -------> used by the SCSI driver
page 4 -------> free

can't be used either. Neither can page three of

page 0 -------> used by
page 1 -------> a big
page 2 -------> network buffer
page 3 -------> would be free if kmalloc didn't use power-of-two
page 4 -------> free

So the new system instantly allows you to allocate a lot more pages. That
might be enough, statistically, if you always reserve a certain percentage
of pages for GPF_ATOMIC (or was that GFP_ATOMIC?) allocations.

An interrupt-safe vmalloc wouldn't exactly be a bad idea either, of course.
Idea: Collect a few of the reserved pages into a reserved memory map,
allocate bigger chunks from the front of the map, and create a kernel
daemon to auto-enlarge the thing if it gets too small, and to really free
the chunks which were only marked free by vfree() because it got called
from an interrupt.

Shouldn't be _too_ difficult.
--
Enough research will tend to confirm your conclusions.
--
Matthias Urlichs \ noris network GmbH / Xlink-POP Nürnberg
Schleiermacherstraße 12 \ Linux+Internet / EMail: urlichs@noris.de
90491 Nürnberg (Germany) \ Consulting+Programming+Networking+etc'ing
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