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Re: [libvirt] [PATCH] qemu: Set swap_hard_limit before hard_limit



On 07/12/2012 11:37 AM, Osier Yang wrote:
> On 2012年07月12日 17:19, Hu Tao wrote:
>> On Thu, Jul 12, 2012 at 05:03:52PM +0800, Osier Yang wrote:
>>> Setting hard_limit larger than previous swap_hard_limit must fail,
>>> it's not that good if one wants to change the swap_hard_limit
>>> and hard_limit together. E.g.
>>>
>>> % virsh memtune rhel6
>>> hard_limit     : 1000000
>>> soft_limit     : 1000000
>>> swap_hard_limit: 1000000
>>>
>>> % virsh memtune rhel6 --hard-limit 1000020 --soft-limit 1000020 \
>>> --swap-hard-limit 1000020 --live
>>>
>>> This patch reoder the limits setting to set the swap_hard_limit
>>> first.
>>> ---
>>>   src/qemu/qemu_driver.c |   26 +++++++++++++-------------
>>>   1 files changed, 13 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
>>> index dc04d13..1abdd27 100644
>>> --- a/src/qemu/qemu_driver.c
>>> +++ b/src/qemu/qemu_driver.c
>>> @@ -6625,43 +6625,43 @@ qemuDomainSetMemoryParameters(virDomainPtr dom,
>>>       for (i = 0; i<  nparams; i++) {
>>>           virTypedParameterPtr param =&params[i];
>>
>> Does this patch make any difference if the order of elements of params[]
>> doesn't change?
> 
> Oops, right. I rushed, except qemu, lxc openvz also support memtune,
> means I need a v2 anyway. Thanks.
> 

One more thing. If the limit goes down it has to be set in the order:
 1. soft_limit
 2. hard_limit
 3. swap_hard_limit

because otherwise you'll get to the same problems. I had something like
this in mind:

for each parameter -- check if it can be set (according to the current
values):
 - yes) set it
 - no) check if the parameter blocking the current one is being changed
as well:
    - no) fail
    - yes) prefer the parameter blocking the current one

Few more approaches (just to get it out of my head):
 - set the values twice with ignoring errors in the first pass (ugly)
 - check and sort all the parameters and then change them (overhead?)
 - set the values to max/unlimited and then set them in a predefined
order (soft, hard, memsw).

Have a nice day,
Martin


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