[Fedora-xen] Re: blkbk/netbk modules fail to load on fedora xen/ia64

[Akio Takebe]

Hi, Aron and all

>> We may have to change dom0_mem of FC6 default to 1GB.
>> But I think the best fix is (1) statically link the modules.
>> (Because all kernel-xen need blkbk/netbk and xenblk/net. 
>> ide module is also static link. And because xen community member
>> test the statically linked modules, I think the statically linked
>> modules is stabler than the dynamic linked modlues.)
>
>I don't mind asking RH to statically link the modules if there is good
>reason.  However I don't understand why it is needed.  512M is a lot
>of memory!  How can it be filled to the extent that the blkbk/netbk
>modules won't load?  What are their requirements?
>

Please see the following error message.
    FATAL: Error inserting blkbk
    (/lib/modules/2.6.17-1.2566.fc6xen/kernel/drivers/xen/
    blkback/blkbk.ko): Cannot allocate memory
    modprobe: page allocation failure. order:8, mode:0xd0

blkbk.ko request order8 pages in blkif_init().
order8 pages is very big.
page_alloc() probably fail when it is requested order8 pages,
because page_alloc() must return contiguos pages.
Especially after boot and terminate some processes,
page_alloc() is hard to allocate order8 pages.

So when dom0_mem=1G, page_allo() is easier to allocate them 
than dom0_mem=512M.
And when statically linked modules, page_alloc() is the easest 
to allocate them.

I think implementation of blk/netbk.ko is not good.
But I think statically linked modules is the best solution in your 
solutions.
And I think this issue is happened in the case of not only ia64,
but also x86.
(In the case of x86, default size of dom0_mem is physcal memory size.
So this issue is hard to be happened.)

Please commets.

FYI
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=202971

Best Regards,

Akio Takebe