[libvirt] [PATCH v2 20/20] qemu: ensure that memory 'discard' is used if specified in XML

[Michal Privoznik]

On 08/09/2018 02:38 PM, Pavel Hrdina wrote:
> Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
> ---
>  src/qemu/qemu_command.c                        |  4 +++-
>  .../pages-discard-hugepages.args               | 11 +++++++----
>  tests/qemuxml2argvdata/pages-discard.args      | 18 ++++++++++++++----
>  3 files changed, 24 insertions(+), 9 deletions(-)
> 
> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> index dbeb3a54f6..a7859feae6 100644
> --- a/src/qemu/qemu_command.c
> +++ b/src/qemu/qemu_command.c
> @@ -3147,6 +3147,7 @@ qemuBuildMemoryBackendProps(virJSONValuePtr *backendProps,
>          return -1;
>  
>      if (useHugepage || mem->nvdimmPath || memAccess ||
> +        discard == VIR_TRISTATE_BOOL_YES ||
>          def->mem.source == VIR_DOMAIN_MEMORY_SOURCE_FILE) {
>  
>          if (useHugepage) {
> @@ -3228,7 +3229,8 @@ qemuBuildMemoryBackendProps(virJSONValuePtr *backendProps,
>      if (!needHugepage && !mem->sourceNodes && !nodeSpecified &&
>          !mem->nvdimmPath &&
>          memAccess == VIR_DOMAIN_MEMORY_ACCESS_DEFAULT &&
> -        def->mem.source != VIR_DOMAIN_MEMORY_SOURCE_FILE && !force) {
> +        def->mem.source != VIR_DOMAIN_MEMORY_SOURCE_FILE && !force &&
> +        discard != VIR_TRISTATE_BOOL_YES) {
>          /* report back that using the new backend is not necessary
>           * to achieve the desired configuration */
>          ret = 1;
> diff --git a/tests/qemuxml2argvdata/pages-discard-hugepages.args b/tests/qemuxml2argvdata/pages-discard-hugepages.args
> index 2dfacefe4a..d859480c26 100644
> --- a/tests/qemuxml2argvdata/pages-discard-hugepages.args
> +++ b/tests/qemuxml2argvdata/pages-discard-hugepages.args
> @@ -10,10 +10,13 @@ QEMU_AUDIO_DRV=none \
>  -machine pc,accel=tcg,usb=off,dump-guest-core=off \
>  -m 1024 \
>  -smp 2,sockets=2,cores=1,threads=1 \
> --mem-prealloc \
> --mem-path /dev/hugepages2M/libvirt/qemu/-1-SomeDummyHugepagesGu \
> --numa node,nodeid=0,cpus=0,mem=256 \
> --numa node,nodeid=1,cpus=1,mem=768 \
> +-object memory-backend-file,id=ram-node0,prealloc=yes,\
> +mem-path=/dev/hugepages2M/libvirt/qemu/-1-SomeDummyHugepagesGu,size=268435456 \
> +-numa node,nodeid=0,cpus=0,memdev=ram-node0 \
> +-object memory-backend-file,id=ram-node1,prealloc=yes,\
> +mem-path=/dev/hugepages2M/libvirt/qemu/-1-SomeDummyHugepagesGu,\
> +discard-data=yes,size=805306368 \
> +-numa node,nodeid=1,cpus=1,memdev=ram-node1 \

This will break migration. But at the same time, it's very unlikely that
anybody is using discard without hugepages.

Michal