[Qemu-devel] [PULL 09/15] pc: count in 1Gb hugepage alignment when sizing hotplug-memory container

["Michael S. Tsirkin" <mst@redhat.com>]

From: Igor Mammedov <imammedo@redhat.com>

if DIMMs with different size/alignment are interleaved
in creation order, it could lead to hotplug-memory
container fragmentation and following inability to use
all RAM upto maxmem.
For example:
    -m 4G,slots=3,maxmem=7G
    -object memory-backend-file,id=mem-1,size=256M,mem-path=/pagesize-2MB
    -device pc-dimm,id=mem1,memdev=mem-1
    -object memory-backend-file,id=mem-2,size=1G,mem-path=/pagesize-1GB
    -device pc-dimm,id=mem2,memdev=mem-2
    -object memory-backend-file,id=mem-3,size=256M,mem-path=/pagesize-2MB
    -device pc-dimm,id=mem3,memdev=mem-3

fragments hotplug-memory container and doesn't allow
to use 1GB hugepage backend to consume remainig 1Gb.

To ease managment factor count in max 1Gb alignment for
each memory slot when sizing hotplug-memory region so
that regadless of fragmentaion it would be possible to
add max aligned DIMM.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/i386/pc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index d448d0d..e656658 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1247,6 +1247,11 @@ FWCfgState *pc_memory_init(MachineState *machine,
         pcms->hotplug_memory_base =
             ROUND_UP(0x100000000ULL + above_4g_mem_size, 1ULL << 30);
 
+        if (pcms->enforce_aligned_dimm) {
+            /* size hotplug region assuming 1G page max alignment per slot */
+            hotplug_mem_size += (1ULL << 30) * machine->ram_slots;
+        }
+
         if ((pcms->hotplug_memory_base + hotplug_mem_size) <
             hotplug_mem_size) {
             error_report("unsupported amount of maximum memory: " RAM_ADDR_FMT,
-- 
MST