Increase MAX_RING_PAGE_ORDER value

[Wescoeur]

Hi, I have a issue concerning the ring size, I would like to modify the default value of MAX_RING_PAGE_ORDER to 4, in theory it's ok it's the max authorized value by the blkfront module.

blktap/include/xen_blkif.h

Line 133 in d2f49df

#define MAX_RING_PAGE_ORDER 3

But I don't understand why I can't boot correctly:

xenbus_probe_frontend: Waiting for devices to initialise: 25s...20s...15s...10s...5s...0s...

Should I change something else? Or is there a bug in blktap when MAX_RING_PAGE_ORDER is equal to 4? Thank you!

[andyhhp]

There isn't any inherent limit. Order 3 is 8 pages, and order 4 is 16. However, you do have to draw a boundary somewhere, because resources aren't unlimited for the domains.

To diagnose the problems further, you need to see what is going wrong in the guest. Get dmesg from the VM, and/or xl dmesg from Xen which might identify if the VM has run out of grants.