Currently ARM UEFI images are typically built as 2MB/768kB flash images for code and variables respectively. These images are both then padded out to 64MB before being loaded by QEMU.
Because the images are 64MB each, QEMU allocates 128MB of memory to read them, and then proceeds to read all 128MB from disk (dirtying the memory). Of this 128MB less than 3MB is useful - the rest is zero padding. On a machine with 100 VMs this wastes over 12GB of memory. This set of patches aims to reclaim the wasted memory by allowing QEMU to respect the size of the flash images and allocate only the necessary memory. This will, of course, require that the flash build process be modified to avoid padding the images to 64MB. Because existing machine types expect the full 128MB reserved for flash to be occupied, do so for machine types older than virt-5.2. The changes are beneficial even in this case, because while the full 128MB of memory is allocated, only that required to actually load the flash images from disk is touched. David Edmondson (5): hw/block: blk_check_size_and_read_all should report backend name hw/block: Flash images can be smaller than the device hw/arm: Convert assertions about flash image size to error_report hw/arm: Flash image mapping follows image size hw/arm: Only minimise flash size on older machines hw/arm/trace-events | 2 + hw/arm/virt-acpi-build.c | 30 ++++++++------ hw/arm/virt.c | 86 +++++++++++++++++++++++++++++----------- hw/block/block.c | 26 ++++++------ include/hw/arm/virt.h | 2 + 5 files changed, 97 insertions(+), 49 deletions(-) -- 2.28.0
