Re: partman-zfs warning template wording
Your tone looks unnecessarily accusational. I gave brief
information because starting an in-depth debate about
the actual technical reasons didn't seem useful. What
matters to the template text in partman-zfs is that ZFS
has trouble with i386, not with 32-bit arches in general.
But if you insist I have no problem with elaborating.
2011/2/8 Philipp Kern <trash@philkern.de>:
> General-purpose registers, yeah, sure. This might create performance
> problems, but i386 is as capable to get the processing done as amd64.
Correct.
> You might run into addressing trouble with virtual memory
> management, due to the size of the caches ZFS wants. But then state
> this instead of refering to unrelated issues at hand.
Correct, although it's just part of the picture.
> Could you elaborate on the MMU bit?
I386 forces the kernel to share virtual address space with
userland. If they were allowed to overlap, a cache flush
would be required with every switch to/from kernel mode.
The default in kFreeBSD for i386 is 1 GiB, which
for some workloads is not enough and will lead to panic.
The ZFS Tuning Guide in upstream wiki [1] recommends
increasing this value to 2 GiB, but this can lead to trouble
with some programs.
TTBOMK this problem doesn't happen on other 32-bit
architectures, where caches are aware of user/kernel
separation, overlap may happen painlessly, and thus
4 GiB space is available (2 GiB are already enough for
ZFS-enabled kernel).
> I'm not aware of huge changes that
> cannot be emulated by PAE, too.
If that works it could be considered, but I heard PAE is
very inefficient. This should be discussed in -bsd.
[1] http://wiki.freebsd.org/ZFSTuningGuide#head-5572047de4f96e082e28f40c3855d7800b9033b2
--
Robert Millan
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