Patchwork [v2] add -machine mem_merge=on|off option

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Submitter Luiz Capitulino
Date June 29, 2012, 2 p.m.
Message ID <20120629110045.2d5c4db6@doriath.home>
Download mbox | patch
Permalink /patch/168109/
State New
Headers show

Comments

Luiz Capitulino - June 29, 2012, 2 p.m.
Allows to disable memory merge support (KSM on Linux), which is enabled
by default otherwise.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---

o v2: improve manpage description

 exec.c          | 19 ++++++++++++++++---
 qemu-config.c   |  4 ++++
 qemu-options.hx |  7 ++++++-
 3 files changed, 26 insertions(+), 4 deletions(-)
Anthony Liguori - June 29, 2012, 2:18 p.m.
On 06/29/2012 09:00 AM, Luiz Capitulino wrote:
> Allows to disable memory merge support (KSM on Linux), which is enabled
> by default otherwise.
>
> Signed-off-by: Luiz Capitulino<lcapitulino@redhat.com>
> ---
>
> o v2: improve manpage description
>
>   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 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);

Just a style thing.  Having a function call that may silently not do what you 
expect it to do is an unfriendly thing.

You should at least name the function something like 'memory_try_enable_merging'

Maybe that's not the best name, but you get the idea at least.

Regards,

Anthony Liguori

>               }
>   #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..15351a5 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 [type=]@var{name}[,prop=@var{value}[,...]]
> @@ -50,6 +51,10 @@ 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.
> +@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
>
Luiz Capitulino - June 29, 2012, 2:21 p.m.
On Fri, 29 Jun 2012 09:18:09 -0500
Anthony Liguori <aliguori@us.ibm.com> wrote:

> On 06/29/2012 09:00 AM, Luiz Capitulino wrote:
> > Allows to disable memory merge support (KSM on Linux), which is enabled
> > by default otherwise.
> >
> > Signed-off-by: Luiz Capitulino<lcapitulino@redhat.com>
> > ---
> >
> > o v2: improve manpage description
> >
> >   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 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);
> 
> Just a style thing.  Having a function call that may silently not do what you 
> expect it to do is an unfriendly thing.
> 
> You should at least name the function something like 'memory_try_enable_merging'
> 
> Maybe that's not the best name, but you get the idea at least.

Agreed, will rename and post v3.

> 
> Regards,
> 
> Anthony Liguori
> 
> >               }
> >   #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..15351a5 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 [type=]@var{name}[,prop=@var{value}[,...]]
> > @@ -50,6 +51,10 @@ 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.
> > +@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
> >
>

Patch

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..15351a5 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 [type=]@var{name}[,prop=@var{value}[,...]]
@@ -50,6 +51,10 @@  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.
+@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