提交 63ed05d2 编写于 作者: P Peter Krempa

qemu: Explain mlock limit size more in detail

Based on Alex's explanation [1] in the recent discussion let's update
the comment explaining the memory lock limit calculation.

[1]
http://www.redhat.com/archives/libvir-list/2015-November/msg00329.html
上级 e7b91c51
......@@ -3645,9 +3645,24 @@ qemuDomainGetMlockLimitBytes(virDomainDefPtr def)
goto done;
}
/* VFIO requires all of the guest's memory to be locked resident, plus some
* amount for IO space. Alex Williamson suggested adding 1GiB for IO space
* just to be safe (some finer tuning might be nice, though). */
/* For device passthrough using VFIO the guest memory and MMIO memory
* regions need to be locked persistent in order to allow DMA.
*
* Currently the below limit is based on assumptions about the x86 platform.
*
* The chosen value of 1GiB below originates from x86 systems where it was
* used as space reserved for the MMIO region for the whole system.
*
* On x86_64 systems the MMIO regions of the IOMMU mapped devices don't
* count towards the locked memory limit since the memory is owned by the
* device. Emulated devices though do count, but the regions are usually
* small. Although it's not guaranteed that the limit will be enough for all
* configurations it didn't pose a problem for now.
*
* http://www.redhat.com/archives/libvir-list/2015-November/msg00329.html
*
* Note that this may not be valid for all platforms.
*/
memKB = virDomainDefGetMemoryActual(def) + 1024 * 1024;
done:
......
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