[Xen-devel] Hard 6 Meg limit on shared pages

[James Pendergrass <James.Pendergrass@xxxxxxxxxx>]

I've been doing some stress testing on how much memory a domain can  
share (after a HD and a NIC front end).
It seems that no matter what I set ORDER_GRANT_FRAMES (in xen/include/ 
asm/grant_table.h) and NR_GRANT_FRAMES
(in linux-2.6-xen/include/xen/gnttab.h) to,  attempting to share 6  
megabytes or more from any one domain causes really terrible
errors which very quickly corrupt the virtual hard disk (I have tried  
allocating up to 32 pages for the grant table and the problems persist).
A sample of the error messages generated by the kernel:
EXT2-fs error (device hda1): ext2_get_inode: unable to read inode  
block - inode=346073, block=688192
end_request: I/O error, dev hda1, sector 5737616
end_request: I/O error, dev hda1, sector 5505536
end_request: I/O error, dev hda1, sector 0
EXT2-fs error (device hda1): ext2_get_inode: unable to read inode  
block - inode=346073, block=688192
end_request: I/O error, dev hda1, sector 5737616
end_request: I/O error, dev hda1, sector 5505536
end_request: I/O error, dev hda1, sector 0
EXT2-fs error (device hda1): ext2_get_inode: unable to read inode  
block - inode=346073, block=688192
(sorry I can't get the first error message generated, it scrolls by  
too quickly and my terminals buffer fills up)
I've tried this on xen-3.0-testing.hg (3.0.2-3), and xen-unstable  
trees with the same results.
I have not managed to find any reason why this should be happening.
Is this a known issue?
Is there any additional information I can provide that would help  
track this down?
Thanks
-aaron

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