Re: [Qemu-devel] [PATCH v5] add -machine mem-merge=on|off option

[Anthony Liguori <aliguori@us.ibm.com>]

Luiz Capitulino <lcapitulino@redhat.com> writes:

> It allows to disable memory merge support (KSM on Linux), which is
> enabled by default otherwise.
>
> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

Applied. Thanks.

Regards,

Anthony Liguori

> ---
>
> v5
>
> - rebase on top of current master
>
>  exec.c          | 19 ++++++++++++++++---
>  qemu-config.c   |  4 ++++
>  qemu-options.hx |  7 ++++++-
>  3 files changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index 5834766..c0fbd5b 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2525,6 +2525,19 @@ void qemu_ram_set_idstr(ram_addr_t addr, const char *name, DeviceState *dev)
>      }
>  }
>  
> +static int memory_try_enable_merging(void *addr, size_t len)
> +{
> +    QemuOpts *opts;
> +
> +    opts = qemu_opts_find(qemu_find_opts("machine"), 0);
> +    if (opts && !qemu_opt_get_bool(opts, "mem-merge", true)) {
> +        /* disabled by the user */
> +        return 0;
> +    }
> +
> +    return qemu_madvise(addr, len, QEMU_MADV_MERGEABLE);
> +}
> +
>  ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
>                                     MemoryRegion *mr)
>  {
> @@ -2544,7 +2557,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
>              new_block->host = file_ram_alloc(new_block, size, mem_path);
>              if (!new_block->host) {
>                  new_block->host = qemu_vmalloc(size);
> -                qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
> +                memory_try_enable_merging(new_block->host, size);
>              }
>  #else
>              fprintf(stderr, "-mem-path option unsupported\n");
> @@ -2559,7 +2572,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
>              } else {
>                  new_block->host = qemu_vmalloc(size);
>              }
> -            qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
> +            memory_try_enable_merging(new_block->host, size);
>          }
>      }
>      new_block->length = size;
> @@ -2689,7 +2702,7 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
>                              length, addr);
>                      exit(1);
>                  }
> -                qemu_madvise(vaddr, length, QEMU_MADV_MERGEABLE);
> +                memory_try_enable_merging(vaddr, length);
>                  qemu_ram_setup_dump(vaddr, length);
>              }
>              return;
> diff --git a/qemu-config.c b/qemu-config.c
> index c05ffbc..75763d3 100644
> --- a/qemu-config.c
> +++ b/qemu-config.c
> @@ -612,6 +612,10 @@ static QemuOptsList qemu_machine_opts = {
>              .name = "dump-guest-core",
>              .type = QEMU_OPT_BOOL,
>              .help = "Include guest memory in  a core dump",
> +        }, {
> +            .name = "mem-merge",
> +            .type = QEMU_OPT_BOOL,
> +            .help = "enable/disable memory merge support",
>          },
>          { /* End of list */ }
>      },
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 3c411c4..90328d0 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -38,7 +38,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
>      "                supported accelerators are kvm, xen, tcg (default: tcg)\n"
>      "                kernel_irqchip=on|off controls accelerated irqchip support\n"
>      "                kvm_shadow_mem=size of KVM shadow MMU\n"
> -    "                dump-guest-core=on|off include guest memory in a core dump (default=on)\n",
> +    "                dump-guest-core=on|off include guest memory in a core dump (default=on)\n"
> +    "                mem-merge=on|off controls memory merge support (default: on)\n",
>      QEMU_ARCH_ALL)
>  STEXI
>  @item -machine [type=]@var{name}[,prop=@var{value}[,...]]
> @@ -57,6 +58,10 @@ Enables in-kernel irqchip support for the chosen accelerator when available.
>  Defines the size of the KVM shadow MMU.
>  @item dump-guest-core=on|off
>  Include guest memory in a core dump. The default is on.
> +@item mem-merge=on|off
> +Enables or disables memory merge support. This feature, when supported by
> +the host, de-duplicates identical memory pages among VMs instances
> +(enabled by default).
>  @end table
>  ETEXI
>  
> -- 
> 1.7.11.2.249.g31c7954.dirty