Re: [Qemu-devel] [RFC] exec: eliminate ram naming issue as migration

[Tan, Jianfeng]

> -----Original Message-----
> From: Tan, Jianfeng
> Sent: Saturday, February 24, 2018 11:08 AM
> To: 'Igor Mammedov'
> Cc: Paolo Bonzini; Jason Wang; Maxime Coquelin; address@hidden;
> Michael S . Tsirkin
> Subject: RE: [Qemu-devel] [RFC] exec: eliminate ram naming issue as
> migration
> 
> Hi Igor and all,
> 
> > -----Original Message-----
> > From: Igor Mammedov [mailto:address@hidden
> > Sent: Thursday, February 8, 2018 7:30 PM
> > To: Tan, Jianfeng
> > Cc: Paolo Bonzini; Jason Wang; Maxime Coquelin; qemu-
> address@hidden;
> > Michael S . Tsirkin
> > Subject: Re: [Qemu-devel] [RFC] exec: eliminate ram naming issue as
> > migration
> >
> [...]
> > > > It could be solved by adding memdev option to machine,
> > > > which would allow to specify backend object. And then on
> > > > top make -mem-path alias new option to clean thing up.
> > >
> > > Do you mean?
> > >
> > > src vm: -m xG
> > > dst vm: -m xG,memdev=pc.ram -object memory-backend-
> file,id=pc.ram,size=xG,mem-path=xxx,share=on ...
> > Yep, I've meant something like it
> >
> > src vm: -m xG,memdev=SHARED_RAM -object memory-backend-
> file,id=SHARED_RAM,size=xG,mem-path=xxx,share=on
> > dst vm: -m xG,memdev=SHARED_RAM -object memory-backend-
> file,id=SHARED_RAM,size=xG,mem-path=xxx,share=on
> 
> After a second thought, I find adding a backend for nonnuma pc RAM is
> roundabout way.
> 
> And we actually have an existing way to add a file-backed RAM: commit
> c902760fb25f ("Add option to use file backed guest memory"). Basically, this
> commit adds two options, --mem-path and --mem-prealloc, without specify
> a backend explicitly.
> 
> So how about just adding a new option --mem-share to decide if that's a
> private memory or shared memory? That seems much straightforward way
> to me; after this change we can migrate like:
> 
> src vm: -m xG
> dst vm: -m xG --mem-path xxx --mem-share
> 

Attach the patch FYI. Look forward to your thoughts.

diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 31612ca..5eaf367 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -127,6 +127,7 @@ extern bool enable_mlock;
 extern uint8_t qemu_extra_params_fw[2];
 extern QEMUClockType rtc_clock;
 extern const char *mem_path;
+extern int mem_share;
 extern int mem_prealloc;
 
 #define MAX_NODES 128
diff --git a/numa.c b/numa.c
index 7b9c33a..322289f 100644
--- a/numa.c
+++ b/numa.c
@@ -456,7 +456,7 @@ static void allocate_system_memory_nonnuma(MemoryRegion 
*mr, Object *owner,
     if (mem_path) {
 #ifdef __linux__
         Error *err = NULL;
-        memory_region_init_ram_from_file(mr, owner, name, ram_size, false,
+        memory_region_init_ram_from_file(mr, owner, name, ram_size, mem_share,
                                          mem_path, &err);
         if (err) {
             error_report_err(err);
diff --git a/qemu-options.hx b/qemu-options.hx
index 678181c..c968c53 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -389,6 +389,15 @@ STEXI
 Allocate guest RAM from a temporarily created file in @var{path}.
 ETEXI
 
+DEF("mem-share", 0, QEMU_OPTION_memshare,
+    "-mem-share   make guest memory shareable (use with -mem-path)\n",
+    QEMU_ARCH_ALL)
+STEXI
address@hidden -mem-share
address@hidden -mem-share
+Make file-backed guest RAM shareable when using -mem-path.
+ETEXI
+
 DEF("mem-prealloc", 0, QEMU_OPTION_mem_prealloc,
     "-mem-prealloc   preallocate guest memory (use with -mem-path)\n",
     QEMU_ARCH_ALL)
diff --git a/vl.c b/vl.c
index 444b750..0ff06c2 100644
--- a/vl.c
+++ b/vl.c
@@ -140,6 +140,7 @@ int display_opengl;
 const char* keyboard_layout = NULL;
 ram_addr_t ram_size;
 const char *mem_path = NULL;
+int mem_share = 0;
 int mem_prealloc = 0; /* force preallocation of physical target memory */
 bool enable_mlock = false;
 int nb_nics;
@@ -3395,6 +3396,9 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_mempath:
                 mem_path = optarg;
                 break;
+            case QEMU_OPTION_memshare:
+                mem_share = 1;
+                break;
             case QEMU_OPTION_mem_prealloc:
                 mem_prealloc = 1;
                 break;