diff mbox series

[v2,9/9] hostmem: Wire up RAM_NORESERVE via "reserve" property

Message ID 20210305101634.10745-10-david@redhat.com
State New
Headers show
Series RAM_NORESERVE, MAP_NORESERVE and hostmem "reserve" property | expand

Commit Message

David Hildenbrand March 5, 2021, 10:16 a.m. UTC 
Let's provide a way to control the use of RAM_NORESERVE via memory
backends using the "reserve" property which defaults to true (old
behavior).

Only POSIX supports setting the flag (and Linux support is checked at
runtime, depending on the setting of "/proc/sys/vm/overcommit_memory").
Windows will bail out.

The target use case is virtio-mem, which dynamically exposes memory
inside a large, sparse memory area to the VM. This essentially allows
avoiding to set "/proc/sys/vm/overcommit_memory == 0") when using
virtio-mem and also supporting hugetlbfs in the future.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 backends/hostmem-file.c  | 11 ++++++-----
 backends/hostmem-memfd.c |  1 +
 backends/hostmem-ram.c   |  1 +
 backends/hostmem.c       | 33 +++++++++++++++++++++++++++++++++
 include/sysemu/hostmem.h |  2 +-
 5 files changed, 42 insertions(+), 6 deletions(-)

Comments

Eduardo Habkost March 5, 2021, 10:14 p.m. UTC | #1 
On Fri, Mar 05, 2021 at 11:16:34AM +0100, David Hildenbrand wrote:
> Let's provide a way to control the use of RAM_NORESERVE via memory
> backends using the "reserve" property which defaults to true (old
> behavior).
> 
> Only POSIX supports setting the flag (and Linux support is checked at
> runtime, depending on the setting of "/proc/sys/vm/overcommit_memory").
> Windows will bail out.
> 
> The target use case is virtio-mem, which dynamically exposes memory
> inside a large, sparse memory area to the VM. This essentially allows
> avoiding to set "/proc/sys/vm/overcommit_memory == 0") when using
> virtio-mem and also supporting hugetlbfs in the future.
> 
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>

Paolo, will the whole series get through your memory API queue?

Also, do you think we should move backends/hostmem* under the
"memory API" section in MAINTAINERS?  Most memory backend changes
also involve changes in the memory API.
diff mbox series

Patch

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index b683da9daf..9d550e53d4 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -40,6 +40,7 @@  file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
                object_get_typename(OBJECT(backend)));
 #else
     HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(backend);
+    uint32_t ram_flags;
     gchar *name;
 
     if (!backend->size) {
@@ -52,11 +53,11 @@  file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
     }
 
     name = host_memory_backend_get_name(backend);
-    memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
-                                     name,
-                                     backend->size, fb->align,
-                                     (backend->share ? RAM_SHARED : 0) |
-                                     (fb->is_pmem ? RAM_PMEM : 0),
+    ram_flags = backend->share ? RAM_SHARED : 0;
+    ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
+    ram_flags |= fb->is_pmem ? RAM_PMEM : 0;
+    memory_region_init_ram_from_file(&backend->mr, OBJECT(backend), name,
+                                     backend->size, fb->align, ram_flags,
                                      fb->mem_path, fb->readonly, errp);
     g_free(name);
 #endif
diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
index 93b5d1a4cf..f3436b623d 100644
--- a/backends/hostmem-memfd.c
+++ b/backends/hostmem-memfd.c
@@ -55,6 +55,7 @@  memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
 
     name = host_memory_backend_get_name(backend);
     ram_flags = backend->share ? RAM_SHARED : 0;
+    ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
     memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), name,
                                    backend->size, ram_flags, fd, 0, errp);
     g_free(name);
diff --git a/backends/hostmem-ram.c b/backends/hostmem-ram.c
index 741e701062..b8e55cdbd0 100644
--- a/backends/hostmem-ram.c
+++ b/backends/hostmem-ram.c
@@ -29,6 +29,7 @@  ram_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
 
     name = host_memory_backend_get_name(backend);
     ram_flags = backend->share ? RAM_SHARED : 0;
+    ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
     memory_region_init_ram_flags_nomigrate(&backend->mr, OBJECT(backend), name,
                                            backend->size, ram_flags, errp);
     g_free(name);
diff --git a/backends/hostmem.c b/backends/hostmem.c
index c6c1ff5b99..4e80162915 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -217,6 +217,11 @@  static void host_memory_backend_set_prealloc(Object *obj, bool value,
     Error *local_err = NULL;
     HostMemoryBackend *backend = MEMORY_BACKEND(obj);
 
+    if (!backend->reserve && value) {
+        error_setg(errp, "'prealloc=on' and 'reserve=off' are incompatible");
+        return;
+    }
+
     if (!host_memory_backend_mr_inited(backend)) {
         backend->prealloc = value;
         return;
@@ -268,6 +273,7 @@  static void host_memory_backend_init(Object *obj)
     /* TODO: convert access to globals to compat properties */
     backend->merge = machine_mem_merge(machine);
     backend->dump = machine_dump_guest_core(machine);
+    backend->reserve = true;
     backend->prealloc_threads = 1;
 }
 
@@ -426,6 +432,28 @@  static void host_memory_backend_set_share(Object *o, bool value, Error **errp)
     backend->share = value;
 }
 
+static bool host_memory_backend_get_reserve(Object *o, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(o);
+
+    return backend->reserve;
+}
+
+static void host_memory_backend_set_reserve(Object *o, bool value, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(o);
+
+    if (host_memory_backend_mr_inited(backend)) {
+        error_setg(errp, "cannot change property value");
+        return;
+    }
+    if (backend->prealloc && !value) {
+        error_setg(errp, "'prealloc=on' and 'reserve=off' are incompatible");
+        return;
+    }
+    backend->reserve = value;
+}
+
 static bool
 host_memory_backend_get_use_canonical_path(Object *obj, Error **errp)
 {
@@ -494,6 +522,11 @@  host_memory_backend_class_init(ObjectClass *oc, void *data)
         host_memory_backend_get_share, host_memory_backend_set_share);
     object_class_property_set_description(oc, "share",
         "Mark the memory as private to QEMU or shared");
+    object_class_property_add_bool(oc, "reserve",
+        host_memory_backend_get_reserve, host_memory_backend_set_reserve);
+    object_class_property_set_description(oc, "reserve",
+        "Reserve swap space (or huge pages under Linux) for the whole memory"
+        " backend, if supported by the OS.");
     /*
      * Do not delete/rename option. This option must be considered stable
      * (as if it didn't have the 'x-' prefix including deprecation period) as
diff --git a/include/sysemu/hostmem.h b/include/sysemu/hostmem.h
index df5644723a..9ff5c16963 100644
--- a/include/sysemu/hostmem.h
+++ b/include/sysemu/hostmem.h
@@ -64,7 +64,7 @@  struct HostMemoryBackend {
     /* protected */
     uint64_t size;
     bool merge, dump, use_canonical_path;
-    bool prealloc, is_mapped, share;
+    bool prealloc, is_mapped, share, reserve;
     uint32_t prealloc_threads;
     DECLARE_BITMAP(host_nodes, MAX_NODES + 1);
     HostMemPolicy policy;