[Bug 197789] (zfs+i386 No PAE) panic: kmem_malloc(36864): kmem_map too small: 431976448 total allocated

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=197789

--- Comment #8 from Michelle Sullivan <michelle at sorbs.net> ---
100% right with the 512MB limit.

Setting arc_max to 40M is ignored... I have that now with a single CPU and it's
showing (in "top"):

Total: 52M 1858K MFU, 24M MRU, 400K Anon, 1975K Header, 24M Other

If I set more than one CPU in the VM - the 'Total' will get to around 467M and
then panic (same loader.conf settings)

This I believe is the bug/a bug...

Running ZFS on i386 should not be recommended, 100% with you... however:

1/ It is available in default kernels.
2/ KVA Pages needs to be set for default kernels. 
3/ I'm not using ZFS in production anywhere - it's used for poudriere otherwise
I'd disable it completely. 

We have a couple of things/statements here:

1/ Its available for use by default, recommended or not.
2/ It seems to work (all be it slowly) on i386 with the correct tuning.
3/ More than one CPU and it doesn't work
4/ KVA pages is not set by default.

At least some should be resolved.... and this is how I see it:

1/ It either should be enabled by default and KVA_PAGES=512 set by default.
2/ It should be disabled by default with the warning that KVA_PAGES needs to be
set if enabling.

and:

A/ someone should look into and resolve (if possible) the fact that arc_max is
not respected when multiple CPUs are present.
B/ documentation to indicating (1) and/or (2) should be updated (currently
there is the link that you indicated, it probably should be expanded to
indicate that ZFS is disabled and KVA_PAGES should be added if enabling, or
that zfs is enabled and so it KVA_PAGES by default and what ever risk that may
entail - it should also probably add that ZFS is really not for i386 because it
will be really slow as it wasn't designed for 32 bit... [does that make
sense?])

Thoughts?

Not trying to be a pain here - but the default should work (even if that's
"Disable ZFS in the default kernel") ...  and I really think that 1 CPU
working, 2 CPU = panic is a bug, and possibly an important one that may even be
there on amd64 just it is not noticed because of the platform difference.

Regards,

Michelle

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