Re: [Qemu-devel] [PATCH] add -machine mem_merge=on|off option

[Jan Kiszka]

On 2012-06-27 18:49, Luiz Capitulino wrote:
> Allows to disable memory merge support (KSM on Linux), which is enabled
> by default otherwise.
> 
> Signed-off-by: Luiz Capitulino <address@hidden>
> ---
>  exec.c          | 19 ++++++++++++++++---
>  qemu-config.c   |  4 ++++
>  qemu-options.hx |  5 ++++-
>  3 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 8244d54..24dd154 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2499,6 +2499,19 @@ void qemu_ram_set_idstr(ram_addr_t addr, const char 
> *name, DeviceState *dev)
>      }
>  }
>  
> +static int madvise_mergeable(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)
>  {
> @@ -2518,7 +2531,7 @@ 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);
> +                madvise_mergeable(new_block->host, size);
>              }
>  #else
>              fprintf(stderr, "-mem-path option unsupported\n");
> @@ -2545,7 +2558,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, 
> void *host,
>                  new_block->host = qemu_vmalloc(size);
>              }
>  #endif
> -            qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
> +            madvise_mergeable(new_block->host, size);
>          }
>      }
>      new_block->length = size;
> @@ -2672,7 +2685,7 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
>                              length, addr);
>                      exit(1);
>                  }
> -                qemu_madvise(vaddr, length, QEMU_MADV_MERGEABLE);
> +                madvise_mergeable(vaddr, length);
>              }
>              return;
>          }
> diff --git a/qemu-config.c b/qemu-config.c
> index 5c3296b..e47612e 100644
> --- a/qemu-config.c
> +++ b/qemu-config.c
> @@ -595,6 +595,10 @@ static QemuOptsList qemu_machine_opts = {
>              .name = "dt_compatible",
>              .type = QEMU_OPT_STRING,
>              .help = "Overrides the \"compatible\" property of the dt root 
> node",
> +        }, {
> +            .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 8b66264..e0e7686 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -33,7 +33,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
>      "                property accel=accel1[:accel2[:...]] selects 
> accelerator\n"
>      "                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",
> +    "                kvm_shadow_mem=size of KVM shadow MMU\n"
> +    "                mem_merge=on|off controls memory merge support 
> (default: on)\n",
>      QEMU_ARCH_ALL)
>  STEXI
>  @item -machine address@hidden,address@hidden,...]]
> @@ -50,6 +51,8 @@ to initialize.
>  Enables in-kernel irqchip support for the chosen accelerator when available.
>  @item kvm_shadow_mem=size
>  Defines the size of the KVM shadow MMU.
> address@hidden mem_merge=on|off
> +Enables or disables memory merge support (enabled by default).

Describe it as memory deduplication? Just a suggestion. Interface looks
good to me now.

Jan

-- 
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Corporate Competence Center Embedded Linux