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Re: [Xen-devel] [PATCH 0 of 4] Handling of (some) low memory conditions

  • To: "Jan Beulich" <JBeulich@xxxxxxxx>
  • From: "Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx>
  • Date: Thu, 16 Feb 2012 07:34:13 -0800
  • Cc: andres@xxxxxxxxxxxxxx, xen-devel <xen-devel@xxxxxxxxxxxxx>, tim@xxxxxxx, adin@xxxxxxxxxxxxxx
  • Delivery-date: Thu, 16 Feb 2012 15:34:43 +0000
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>>>> On 16.02.12 at 15:40, "Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx>
>>>> wrote:
>>>>>> On 16.02.12 at 04:57, Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
>>>>>> wrote:
>>>> - Add a VIRQ that the hypervisor can emit when reaching a low memory
>>>> threshold.
>>> In this patch, which didn't make it to my inbox yet, you will want to
>>> change this
>>> +    if ( (total_avail_pages << PAGE_SHIFT) <= opt_low_mem_virq )
>>> to
>>>     if ( total_avail_pages <= PFN_DOWN(opt_low_mem_virq) )
>>> to avoid the case (on 32-bit hypervisors) where total_avail_pages,
>>> being just 'long', would get significant bits shifted out.
>>> I'm further wondering whether the default value shouldn't be set
>>> dynamically based on available memory and/or taking into account
>>> an eventual dom0_mem= option.
>> I can cap or get rid of the threshold (and the virq) if it doesn't make
>> sense with respect to total memory. I'm not sure about integrating
>> dom0_mem, since dom0's footprint is also a quantity manipulated by the
>> receiver of the virq.
> No, dom0_mem= is only specifying the starting value, and the case
> that would be of possibly interest is that of having a negative amount
> specified.

Sorry, not following entirely. The negative quantity you refer to would be
dom0_mem or the low mem virq threshold? Additional checks pertaining only
to dom0_mem, not in relation to this threshold, would most likely go on a
separate patch.

And both quantities are parsed using strtoull, so you get at most really
large numbers. I certainly need to add additional checks for unsuitable
low_mem_virq thresholds to this patch.

> Jan

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