Re: [Qemu-devel] [PATCH v3] memory: add -machine dump-guest-core=on|off

[Markus Armbruster]

Jason Baron <address@hidden> writes:

> Add a new '[,dump-guest-core=on|off]' option to the '-machine' option. When
> 'dump-guest-core=off' is specified, guest memory is omitted from the core 
> dump.
> The default behavior continues to be to include guest memory when a core dump 
> is
> triggered. In my testing, this brought the core dump size down from 384MB to 
> 6MB
> on a 2GB guest.
>
> Is anything additional required to preserve this setting for migration or
> savevm? I don't believe so.
>
> Changelog:
> v3:
>     Eliminate globals as per Anthony's suggestion
>     set no dump from qemu_ram_remap() as well
> v2:
>     move the option from -m to -machine, rename option dump -> dump-guest-core
>
> Signed-off-by: Jason Baron <address@hidden>
> ---
>  exec.c          |   21 +++++++++++++++++++++
>  osdep.h         |    7 +++++++
>  qemu-config.c   |    4 ++++
>  qemu-options.hx |    5 ++++-
>  4 files changed, 36 insertions(+), 1 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index feb4795..4152422 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2478,6 +2478,24 @@ static ram_addr_t last_ram_offset(void)
>      return last;
>  }
>  
> +static void qemu_ram_setup_dump(void *addr, ram_addr_t size)
> +{
> +    int ret;
> +    QemuOpts *machine_opts;
> +
> +    /* Use MADV_DONTDUMP, if user doesn't want the guest memory in the core 
> */
> +    machine_opts = qemu_opts_find(qemu_find_opts("machine"), 0);
> +    if (machine_opts &&
> +        !qemu_opt_get_bool(machine_opts, "dump-guest-core", true)) {
> +        ret = qemu_madvise(addr, size, QEMU_MADV_DONTDUMP);
> +        if (ret) {
> +            perror("qemu_madvise");
> +            fprintf(stderr, "madvise doesn't support MADV_DONTDUMP, "
> +                            "but dump_guest_core=off specified\n");
> +        }
> +    }
> +}
> +
>  void qemu_ram_set_idstr(ram_addr_t addr, const char *name, DeviceState *dev)
>  {
>      RAMBlock *new_block, *block;
> @@ -2555,6 +2573,8 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, 
> void *host,
>                                         last_ram_offset() >> 
> TARGET_PAGE_BITS);
>      cpu_physical_memory_set_dirty_range(new_block->offset, size, 0xff);
>  
> +    qemu_ram_setup_dump(new_block->host, size);
> +
>      if (kvm_enabled())
>          kvm_setup_guest_memory(new_block->host, size);
>  
> @@ -2671,6 +2691,7 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
>                      exit(1);
>                  }
>                  qemu_madvise(vaddr, length, QEMU_MADV_MERGEABLE);
> +                qemu_ram_setup_dump(vaddr, length);
>              }
>              return;
>          }
> diff --git a/osdep.h b/osdep.h
> index 1e15a4b..e2d0f57 100644
> --- a/osdep.h
> +++ b/osdep.h
> @@ -102,6 +102,11 @@ void qemu_vfree(void *ptr);
>  #else
>  #define QEMU_MADV_MERGEABLE QEMU_MADV_INVALID
>  #endif
> +#ifdef MADV_DONTDUMP
> +#define QEMU_MADV_DONTDUMP MADV_DONTDUMP
> +#else
> +#define QEMU_MADV_DONTDUMP QEMU_MADV_INVALID
> +#endif
>  
>  #elif defined(CONFIG_POSIX_MADVISE)
>  
> @@ -109,6 +114,7 @@ void qemu_vfree(void *ptr);
>  #define QEMU_MADV_DONTNEED  POSIX_MADV_DONTNEED
>  #define QEMU_MADV_DONTFORK  QEMU_MADV_INVALID
>  #define QEMU_MADV_MERGEABLE QEMU_MADV_INVALID
> +#define QEMU_MADV_DONTDUMP QEMU_MADV_INVALID
>  
>  #else /* no-op */
>  
> @@ -116,6 +122,7 @@ void qemu_vfree(void *ptr);
>  #define QEMU_MADV_DONTNEED  QEMU_MADV_INVALID
>  #define QEMU_MADV_DONTFORK  QEMU_MADV_INVALID
>  #define QEMU_MADV_MERGEABLE QEMU_MADV_INVALID
> +#define QEMU_MADV_DONTDUMP QEMU_MADV_INVALID
>  
>  #endif
>  
> diff --git a/qemu-config.c b/qemu-config.c
> index 5c3296b..6700de0 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 = "dump-guest-core",
> +            .type = QEMU_OPT_BOOL,
> +            .help = "Include guest memory in  a core dump",
>          },
>          { /* End of list */ }
>      },
> diff --git a/qemu-options.hx b/qemu-options.hx
> index dc68e15..a3244d7 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"
> +    "                dump-guest-core=on|off include guest memory in a core 
> dump (default=on)\n",

I'd ask you to limit help line length to 80 characters, except there are
so many offenders already that one more can't make it worse than it
already is.

>      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 dump-guest-core=on|off
> +Include guest memory in a core dump. The default is on.
>  @end table
>  ETEXI

Looks good to me.