[Xen-devel] 2.6.28 and balloon driver

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

I am playing with 2.6.28 on xen.  Nice!  Thanks Jeremy!

But I have a minor gripe...

The balloon driver now is accessed via a sysfs file, for example:

# SIZE=`cat /sys/devices/system/xen_memory/xen_memory0/target_kb`
# echo $SIZE
# echo $SIZE > /sys/devices/system/xen_memory/xen_memory0/target_kb

SIZE does indeed get current memory size in kbytes, but
if one tries to pass SIZE (or slightly smaller value) back,
all hell breaks loose because:

1) Despite the name, the value written must be in bytes, not kbytes
2) There is no "safety minimum", so writing the same value back
   actually reduces memory by a factor of 1024!

I realize behavior (1) is backwards-compatible with the existing
/proc/xen/balloon behavior, but at least that filename doesn't
imply a unit size.

For (2), as sysadmins grow comfortable with the "safety minimum"
that's been implemented in upstream xen now for nearly a year,
(users can do:

# echo 0 > /proc/xen/balloon

and it still works), some people upgrading to a 2.6.28 kernel
are in for a nasty surprise.

<gripe off>

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