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[Qemu-devel] [PULL 03/12] hostmem-file: Add "discard-data" option
From: |
Eduardo Habkost |
Subject: |
[Qemu-devel] [PULL 03/12] hostmem-file: Add "discard-data" option |
Date: |
Tue, 19 Sep 2017 17:18:41 -0300 |
The new option can be used to indicate that the file contents can
be destroyed and don't need to be flushed to disk when QEMU exits
or when the memory backend object is removed.
Internally, it will trigger a madvise(MADV_REMOVE) call when the
memory backend is removed.
Signed-off-by: Eduardo Habkost <address@hidden>
Message-Id: <address@hidden>
[ehabkost: fixup: improved documentation]
Reviewed-by: Daniel P. Berrange <address@hidden>
Tested-by: Zack Cornelius <address@hidden>
Signed-off-by: Eduardo Habkost <address@hidden>
---
backends/hostmem-file.c | 29 +++++++++++++++++++++++++++++
qemu-options.hx | 8 +++++++-
2 files changed, 36 insertions(+), 1 deletion(-)
diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index fc4ef46d11..e44c319915 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -32,6 +32,7 @@ struct HostMemoryBackendFile {
HostMemoryBackend parent_obj;
bool share;
+ bool discard_data;
char *mem_path;
};
@@ -103,16 +104,44 @@ static void file_memory_backend_set_share(Object *o, bool
value, Error **errp)
fb->share = value;
}
+static bool file_memory_backend_get_discard_data(Object *o, Error **errp)
+{
+ return MEMORY_BACKEND_FILE(o)->discard_data;
+}
+
+static void file_memory_backend_set_discard_data(Object *o, bool value,
+ Error **errp)
+{
+ MEMORY_BACKEND_FILE(o)->discard_data = value;
+}
+
+static void file_backend_unparent(Object *obj)
+{
+ HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+ HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
+
+ if (host_memory_backend_mr_inited(backend) && fb->discard_data) {
+ void *ptr = memory_region_get_ram_ptr(&backend->mr);
+ uint64_t sz = memory_region_size(&backend->mr);
+
+ qemu_madvise(ptr, sz, QEMU_MADV_REMOVE);
+ }
+}
+
static void
file_backend_class_init(ObjectClass *oc, void *data)
{
HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
bc->alloc = file_backend_memory_alloc;
+ oc->unparent = file_backend_unparent;
object_class_property_add_bool(oc, "share",
file_memory_backend_get_share, file_memory_backend_set_share,
&error_abort);
+ object_class_property_add_bool(oc, "discard-data",
+ file_memory_backend_get_discard_data,
file_memory_backend_set_discard_data,
+ &error_abort);
object_class_property_add_str(oc, "mem-path",
get_mem_path, set_mem_path,
&error_abort);
diff --git a/qemu-options.hx b/qemu-options.hx
index 600614f6e5..77859a248c 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4182,7 +4182,7 @@ property must be set. These objects are placed in the
@table @option
address@hidden -object
memory-backend-file,address@hidden,address@hidden,address@hidden,address@hidden|off}
address@hidden -object
memory-backend-file,address@hidden,address@hidden,address@hidden,address@hidden|off},address@hidden|off}
Creates a memory file backend object, which can be used to back
the guest RAM with huge pages. The @option{id} parameter is a
@@ -4194,6 +4194,12 @@ the path to either a shared memory or huge page
filesystem mount.
The @option{share} boolean option determines whether the memory
region is marked as private to QEMU, or shared. The latter allows
a co-operating external process to access the QEMU memory region.
+Setting the @option{discard-data} boolean option to @var{on}
+indicates that file contents can be destroyed when QEMU exits,
+to avoid unnecessarily flushing data to the backing file. Note
+that @option{discard-data} is only an optimization, and QEMU
+might not discard file contents if it aborts unexpectedly or is
+terminated using SIGKILL.
@item -object rng-random,address@hidden,address@hidden/dev/random}
--
2.13.5
- [Qemu-devel] [PULL 00/12] Machine/CPU/NUMA queue, 2017-09-19, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 01/12] vl: Clean up user-creatable objects when exiting, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 02/12] osdep: Define QEMU_MADV_REMOVE, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 03/12] hostmem-file: Add "discard-data" option,
Eduardo Habkost <=
- [Qemu-devel] [PULL 04/12] qom: cpus: split cpu_generic_init() on feature parsing and cpu creation parts, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 05/12] cpu: make cpu_generic_init() abort QEMU on error, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 06/12] vl.c: convert cpu_model to cpu type and set of global properties before machine_init(), Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 07/12] pc: use generic cpu_model parsing, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 08/12] arm: drop intermediate cpu_model -> cpu type parsing and use cpu type directly, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 09/12] numa: cpu: calculate/set default node-ids after all -numa CLI options are parsed, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 10/12] NUMA: Replace MAX_NODES with nb_numa_nodes in for loop, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 11/12] hw/acpi-build: Fix SRAT memory building in case of node 0 without RAM, Eduardo Habkost, 2017/09/19
- [Qemu-devel] [PULL 12/12] MAINTAINERS: Update git URLs for my trees, Eduardo Habkost, 2017/09/19
- Re: [Qemu-devel] [PULL 00/12] Machine/CPU/NUMA queue, 2017-09-19, Peter Maydell, 2017/09/20