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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Finally, rate limiting will be needed for sending the vIRQ - currently,
once below the threshold you're sending one on each and every
allocation (which may become harmful if the listener can't really do
anything about the situation).

Jan


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