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

[Luiz Capitulino]

On Thu, 28 Jun 2012 11:25:10 +0200
Jan Kiszka <address@hidden> wrote:

> 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.

I can extend the manpage description to read:

 Enables or disables memory merge support. This feature, when supported by
 the host, de-duplicates identical memory pages among VMs instances.
 (enabled by default).