This option controls whether QEMU mmap(2) the memory backend file with
MAP_SYNC flag, which can fully guarantee the guest write persistence
to the backend, if MAP_SYNC flag is supported by the host kernel
(Linux kernel 4.15 and later) and the backend is a file supporting
DAX (e.g., file on ext4/xfs file system mounted with '-o dax').
It can take one of following values:
- on: try to pass MAP_SYNC to mmap(2); if MAP_SYNC is not supported or
'share=off', QEMU will abort
- off: never pass MAP_SYNC to mmap(2)
- auto (default): if MAP_SYNC is supported and 'share=on', work as if
'sync=on'; otherwise, work as if 'sync=off'
Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
Sugguested-by: Eduardo Habkost <ehabkost@redhat.com>
---
backends/hostmem-file.c | 39 ++++++++++++++++++++++++++++++++++++++-
docs/nvdimm.txt | 15 ++++++++++++++-
exec.c | 13 ++++++++-----
include/exec/memory.h | 4 ++++
include/exec/ram_addr.h | 6 +++---
memory.c | 6 ++++--
numa.c | 2 +-
qemu-options.hx | 21 ++++++++++++++++++++-
8 files changed, 92 insertions(+), 14 deletions(-)
diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index e319ec1ad8..52fdc0a48a 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -15,6 +15,7 @@
#include "sysemu/hostmem.h"
#include "sysemu/sysemu.h"
#include "qom/object_interfaces.h"
+#include "qapi-visit.h"
/* hostmem-file.c */
/**
@@ -35,6 +36,7 @@ struct HostMemoryBackendFile {
bool discard_data;
char *mem_path;
uint64_t align;
+ OnOffAuto sync;
};
static void
@@ -60,7 +62,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
path,
backend->size, fb->align, fb->share,
- fb->mem_path, errp);
+ fb->sync, fb->mem_path, errp);
g_free(path);
}
#endif
@@ -150,6 +152,38 @@ static void file_memory_backend_set_align(Object *o, Visitor *v,
error_propagate(errp, local_err);
}
+static void file_memory_backend_get_sync(
+ Object *obj, Visitor *v, const char *name, void *opaque, Error **errp)
+{
+ HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
+ OnOffAuto value = fb->sync;
+
+ visit_type_OnOffAuto(v, name, &value, errp);
+}
+
+static void file_memory_backend_set_sync(
+ Object *obj, Visitor *v, const char *name, void *opaque, Error **errp)
+{
+ HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+ HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
+ Error *local_err = NULL;
+ OnOffAuto value;
+
+ if (host_memory_backend_mr_inited(backend)) {
+ error_setg(&local_err, "cannot change property value");
+ goto out;
+ }
+
+ visit_type_OnOffAuto(v, name, &value, &local_err);
+ if (local_err) {
+ goto out;
+ }
+ fb->sync = value;
+
+ out:
+ error_propagate(errp, local_err);
+}
+
static void file_backend_unparent(Object *obj)
{
HostMemoryBackend *backend = MEMORY_BACKEND(obj);
@@ -184,6 +218,9 @@ file_backend_class_init(ObjectClass *oc, void *data)
file_memory_backend_get_align,
file_memory_backend_set_align,
NULL, NULL, &error_abort);
+ object_class_property_add(oc, "sync", "OnOffAuto",
+ file_memory_backend_get_sync, file_memory_backend_set_sync,
+ NULL, NULL, &error_abort);
}
static void file_backend_instance_finalize(Object *o)
diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
index e903d8bb09..49b174fe66 100644
--- a/docs/nvdimm.txt
+++ b/docs/nvdimm.txt
@@ -143,10 +143,23 @@ Guest Data Persistence
----------------------
Though QEMU supports multiple types of vNVDIMM backends on Linux,
-currently the only one that can guarantee the guest write persistence
+if MAP_SYNC is not supported by the host kernel and the backends,
+the only backend that can guarantee the guest write persistence
is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to
which all guest access do not involve any host-side kernel cache.
+mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such
+systems, QEMU can mmap(2) the backend with MAP_SYNC, which can
+guarantee the guest write persistence to vNVDIMM. Besides the host
+kernel support, enabling MAP_SYNC in QEMU also requires:
+
+ - the backend is a file supporting DAX, e.g., a file on an ext4 or
+ xfs file system mounted with "-o dax",
+
+ - 'sync' option of memory-backend-file is not 'off', and
+
+ - 'share' option of memory-backend-file is 'on'.
+
When using other types of backends, it's suggested to set 'unarmed'
option of '-device nvdimm' to 'on', which sets the unarmed flag of the
guest NVDIMM region mapping structure. This unarmed flag indicates
diff --git a/exec.c b/exec.c
index f4254cb6d3..ce13f8cb21 100644
--- a/exec.c
+++ b/exec.c
@@ -1600,6 +1600,7 @@ static void *file_ram_alloc(RAMBlock *block,
ram_addr_t memory,
int fd,
bool truncate,
+ OnOffAuto sync,
Error **errp)
{
void *area;
@@ -1646,7 +1647,7 @@ static void *file_ram_alloc(RAMBlock *block,
}
area = qemu_ram_mmap(fd, memory, block->mr->align,
- block->flags & RAM_SHARED, ON_OFF_AUTO_OFF);
+ block->flags & RAM_SHARED, sync);
if (area == MAP_FAILED) {
error_setg_errno(errp, errno,
"unable to map backing store for guest RAM");
@@ -1974,7 +1975,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
#ifdef __linux__
RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
- bool share, int fd,
+ bool share, OnOffAuto sync, int fd,
Error **errp)
{
RAMBlock *new_block;
@@ -2017,7 +2018,8 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
new_block->used_length = size;
new_block->max_length = size;
new_block->flags = share ? RAM_SHARED : 0;
- new_block->host = file_ram_alloc(new_block, size, fd, !file_size, errp);
+ new_block->host = file_ram_alloc(new_block, size, fd, !file_size, sync,
+ errp);
if (!new_block->host) {
g_free(new_block);
return NULL;
@@ -2035,7 +2037,8 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
- bool share, const char *mem_path,
+ bool share, OnOffAuto sync,
+ const char *mem_path,
Error **errp)
{
int fd;
@@ -2047,7 +2050,7 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
return NULL;
}
- block = qemu_ram_alloc_from_fd(size, mr, share, fd, errp);
+ block = qemu_ram_alloc_from_fd(size, mr, share, sync, fd, errp);
if (!block) {
if (created) {
unlink(mem_path);
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 07c5d6d597..ff3cd583e9 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -468,6 +468,9 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
* @align: alignment of the region base address; if 0, the default alignment
* (getpagesize()) will be used.
* @share: %true if memory must be mmaped with the MAP_SHARED flag
+ * @sync: %ON_OFF_AUTO_ON if memory must be mapped with MAP_SYNC flag;
+ * %ON_OFF_AUTO_OFF if memory cannot be mapped with MAP_SYNC flag;
+ * %ON_OFF_AUTO_AUTO directs QEMU to mmap with MAP_SYNC flag if possible
* @path: the path in which to allocate the RAM.
* @errp: pointer to Error*, to store an error if it happens.
*
@@ -480,6 +483,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
uint64_t size,
uint64_t align,
bool share,
+ OnOffAuto sync,
const char *path,
Error **errp);
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index 6cbc02aa0f..4494ae9132 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -73,10 +73,10 @@ static inline unsigned long int ramblock_recv_bitmap_offset(void *host_addr,
long qemu_getrampagesize(void);
unsigned long last_ram_page(void);
RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
- bool share, const char *mem_path,
- Error **errp);
+ bool share, OnOffAuto sync,
+ const char *mem_path, Error **errp);
RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
- bool share, int fd,
+ bool share, OnOffAuto sync, int fd,
Error **errp);
RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
MemoryRegion *mr, Error **errp);
diff --git a/memory.c b/memory.c
index 449a1429b9..e22f51394e 100644
--- a/memory.c
+++ b/memory.c
@@ -1572,6 +1572,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
uint64_t size,
uint64_t align,
bool share,
+ OnOffAuto sync,
const char *path,
Error **errp)
{
@@ -1580,7 +1581,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
mr->terminates = true;
mr->destructor = memory_region_destructor_ram;
mr->align = align;
- mr->ram_block = qemu_ram_alloc_from_file(size, mr, share, path, errp);
+ mr->ram_block = qemu_ram_alloc_from_file(size, mr, share, sync, path, errp);
mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
}
@@ -1596,7 +1597,8 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
mr->ram = true;
mr->terminates = true;
mr->destructor = memory_region_destructor_ram;
- mr->ram_block = qemu_ram_alloc_from_fd(size, mr, share, fd, errp);
+ mr->ram_block = qemu_ram_alloc_from_fd(size, mr, share, ON_OFF_AUTO_OFF, fd,
+ errp);
mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
}
#endif
diff --git a/numa.c b/numa.c
index 83675a03f3..93180510a4 100644
--- a/numa.c
+++ b/numa.c
@@ -457,7 +457,7 @@ static void allocate_system_memory_nonnuma(MemoryRegion *mr, Object *owner,
#ifdef __linux__
Error *err = NULL;
memory_region_init_ram_from_file(mr, owner, name, ram_size, 0, false,
- mem_path, &err);
+ ON_OFF_AUTO_OFF, mem_path, &err);
if (err) {
error_report_err(err);
if (mem_prealloc) {
diff --git a/qemu-options.hx b/qemu-options.hx
index 5ff741a4af..3ee423e6a8 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3974,7 +3974,7 @@ property must be set. These objects are placed in the
@table @option
-@item -object memory-backend-file,id=@var{id},size=@var{size},mem-path=@var{dir},share=@var{on|off},discard-data=@var{on|off},merge=@var{on|off},dump=@var{on|off},prealloc=@var{on|off},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave},align=@var{align}
+@item -object memory-backend-file,id=@var{id},size=@var{size},mem-path=@var{dir},share=@var{on|off},discard-data=@var{on|off},merge=@var{on|off},dump=@var{on|off},prealloc=@var{on|off},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave},align=@var{align},sync=@var{on|off|auto}
Creates a memory file backend object, which can be used to back
the guest RAM with huge pages.
@@ -4034,6 +4034,25 @@ requires an alignment different than the default one used by QEMU, eg
the device DAX /dev/dax0.0 requires 2M alignment rather than 4K. In
such cases, users can specify the required alignment via this option.
+The @option{sync} option specifies whether QEMU mmap(2) @option{mem-path}
+with MAP_SYNC flag, which can fully guarantee the guest write
+persistence to @option{mem-path}. MAP_SYNC requires supports from both
+the host kernel (since Linux kernel 4.15) and @option{mem-path} (only
+files supporting DAX). It can take one of following values:
+
+@table @option
+@item @var{on}
+try to pass MAP_SYNC to mmap(2); if MAP_SYNC is not supported or
+@option{share}=@var{off}, QEMU will abort
+
+@item @var{off}
+never pass MAP_SYNC to mmap(2)
+
+@item @var{auto} (default)
+if MAP_SYNC is supported and @option{share}=@var{on}, work as if
+@option{sync}=@var{on}; otherwise, work as if @option{sync}=@var{off}
+@end table
+
@item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave}
Creates a memory backend object, which can be used to back the guest RAM.
--
2.15.1
* Haozhong Zhang (haozhong.zhang@intel.com) wrote:
> This option controls whether QEMU mmap(2) the memory backend file with
> MAP_SYNC flag, which can fully guarantee the guest write persistence
> to the backend, if MAP_SYNC flag is supported by the host kernel
> (Linux kernel 4.15 and later) and the backend is a file supporting
> DAX (e.g., file on ext4/xfs file system mounted with '-o dax').
>
> It can take one of following values:
> - on: try to pass MAP_SYNC to mmap(2); if MAP_SYNC is not supported or
> 'share=off', QEMU will abort
> - off: never pass MAP_SYNC to mmap(2)
> - auto (default): if MAP_SYNC is supported and 'share=on', work as if
> 'sync=on'; otherwise, work as if 'sync=off'
I don't know anything about MAP_SYNC but see two minor comments below:
> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> Sugguested-by: Eduardo Habkost <ehabkost@redhat.com>
^ typo!
> ---
> backends/hostmem-file.c | 39 ++++++++++++++++++++++++++++++++++++++-
> docs/nvdimm.txt | 15 ++++++++++++++-
> exec.c | 13 ++++++++-----
> include/exec/memory.h | 4 ++++
> include/exec/ram_addr.h | 6 +++---
> memory.c | 6 ++++--
> numa.c | 2 +-
> qemu-options.hx | 21 ++++++++++++++++++++-
> 8 files changed, 92 insertions(+), 14 deletions(-)
>
> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> index e319ec1ad8..52fdc0a48a 100644
> --- a/backends/hostmem-file.c
> +++ b/backends/hostmem-file.c
> @@ -15,6 +15,7 @@
> #include "sysemu/hostmem.h"
> #include "sysemu/sysemu.h"
> #include "qom/object_interfaces.h"
> +#include "qapi-visit.h"
>
> /* hostmem-file.c */
> /**
> @@ -35,6 +36,7 @@ struct HostMemoryBackendFile {
> bool discard_data;
> char *mem_path;
> uint64_t align;
> + OnOffAuto sync;
> };
>
> static void
> @@ -60,7 +62,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
> memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
> path,
> backend->size, fb->align, fb->share,
> - fb->mem_path, errp);
> + fb->sync, fb->mem_path, errp);
> g_free(path);
> }
> #endif
> @@ -150,6 +152,38 @@ static void file_memory_backend_set_align(Object *o, Visitor *v,
> error_propagate(errp, local_err);
> }
>
> +static void file_memory_backend_get_sync(
> + Object *obj, Visitor *v, const char *name, void *opaque, Error **errp)
> +{
> + HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
> + OnOffAuto value = fb->sync;
> +
> + visit_type_OnOffAuto(v, name, &value, errp);
> +}
> +
> +static void file_memory_backend_set_sync(
> + Object *obj, Visitor *v, const char *name, void *opaque, Error **errp)
> +{
> + HostMemoryBackend *backend = MEMORY_BACKEND(obj);
> + HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
> + Error *local_err = NULL;
> + OnOffAuto value;
> +
> + if (host_memory_backend_mr_inited(backend)) {
> + error_setg(&local_err, "cannot change property value");
Please make this error clearer; if I was helping someone and saw
this error message in a log, I wouldn't know what type of property it
was on what device. Please at least include something saying it's
memory backend related and sync related; even just including a %s and
__func__ would help; even better if you include the name of the object
so if you had multiple backend files and one failed you could see which
one.
Dave
> + goto out;
> + }
> +
> + visit_type_OnOffAuto(v, name, &value, &local_err);
> + if (local_err) {
> + goto out;
> + }
> + fb->sync = value;
> +
> + out:
> + error_propagate(errp, local_err);
> +}
> +
> static void file_backend_unparent(Object *obj)
> {
> HostMemoryBackend *backend = MEMORY_BACKEND(obj);
> @@ -184,6 +218,9 @@ file_backend_class_init(ObjectClass *oc, void *data)
> file_memory_backend_get_align,
> file_memory_backend_set_align,
> NULL, NULL, &error_abort);
> + object_class_property_add(oc, "sync", "OnOffAuto",
> + file_memory_backend_get_sync, file_memory_backend_set_sync,
> + NULL, NULL, &error_abort);
> }
>
> static void file_backend_instance_finalize(Object *o)
> diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
> index e903d8bb09..49b174fe66 100644
> --- a/docs/nvdimm.txt
> +++ b/docs/nvdimm.txt
> @@ -143,10 +143,23 @@ Guest Data Persistence
> ----------------------
>
> Though QEMU supports multiple types of vNVDIMM backends on Linux,
> -currently the only one that can guarantee the guest write persistence
> +if MAP_SYNC is not supported by the host kernel and the backends,
> +the only backend that can guarantee the guest write persistence
> is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to
> which all guest access do not involve any host-side kernel cache.
>
> +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such
> +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can
> +guarantee the guest write persistence to vNVDIMM. Besides the host
> +kernel support, enabling MAP_SYNC in QEMU also requires:
> +
> + - the backend is a file supporting DAX, e.g., a file on an ext4 or
> + xfs file system mounted with "-o dax",
> +
> + - 'sync' option of memory-backend-file is not 'off', and
> +
> + - 'share' option of memory-backend-file is 'on'.
> +
> When using other types of backends, it's suggested to set 'unarmed'
> option of '-device nvdimm' to 'on', which sets the unarmed flag of the
> guest NVDIMM region mapping structure. This unarmed flag indicates
> diff --git a/exec.c b/exec.c
> index f4254cb6d3..ce13f8cb21 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1600,6 +1600,7 @@ static void *file_ram_alloc(RAMBlock *block,
> ram_addr_t memory,
> int fd,
> bool truncate,
> + OnOffAuto sync,
> Error **errp)
> {
> void *area;
> @@ -1646,7 +1647,7 @@ static void *file_ram_alloc(RAMBlock *block,
> }
>
> area = qemu_ram_mmap(fd, memory, block->mr->align,
> - block->flags & RAM_SHARED, ON_OFF_AUTO_OFF);
> + block->flags & RAM_SHARED, sync);
> if (area == MAP_FAILED) {
> error_setg_errno(errp, errno,
> "unable to map backing store for guest RAM");
> @@ -1974,7 +1975,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
>
> #ifdef __linux__
> RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
> - bool share, int fd,
> + bool share, OnOffAuto sync, int fd,
> Error **errp)
> {
> RAMBlock *new_block;
> @@ -2017,7 +2018,8 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
> new_block->used_length = size;
> new_block->max_length = size;
> new_block->flags = share ? RAM_SHARED : 0;
> - new_block->host = file_ram_alloc(new_block, size, fd, !file_size, errp);
> + new_block->host = file_ram_alloc(new_block, size, fd, !file_size, sync,
> + errp);
> if (!new_block->host) {
> g_free(new_block);
> return NULL;
> @@ -2035,7 +2037,8 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
>
>
> RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
> - bool share, const char *mem_path,
> + bool share, OnOffAuto sync,
> + const char *mem_path,
> Error **errp)
> {
> int fd;
> @@ -2047,7 +2050,7 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
> return NULL;
> }
>
> - block = qemu_ram_alloc_from_fd(size, mr, share, fd, errp);
> + block = qemu_ram_alloc_from_fd(size, mr, share, sync, fd, errp);
> if (!block) {
> if (created) {
> unlink(mem_path);
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 07c5d6d597..ff3cd583e9 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -468,6 +468,9 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
> * @align: alignment of the region base address; if 0, the default alignment
> * (getpagesize()) will be used.
> * @share: %true if memory must be mmaped with the MAP_SHARED flag
> + * @sync: %ON_OFF_AUTO_ON if memory must be mapped with MAP_SYNC flag;
> + * %ON_OFF_AUTO_OFF if memory cannot be mapped with MAP_SYNC flag;
> + * %ON_OFF_AUTO_AUTO directs QEMU to mmap with MAP_SYNC flag if possible
> * @path: the path in which to allocate the RAM.
> * @errp: pointer to Error*, to store an error if it happens.
> *
> @@ -480,6 +483,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
> uint64_t size,
> uint64_t align,
> bool share,
> + OnOffAuto sync,
> const char *path,
> Error **errp);
>
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index 6cbc02aa0f..4494ae9132 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -73,10 +73,10 @@ static inline unsigned long int ramblock_recv_bitmap_offset(void *host_addr,
> long qemu_getrampagesize(void);
> unsigned long last_ram_page(void);
> RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
> - bool share, const char *mem_path,
> - Error **errp);
> + bool share, OnOffAuto sync,
> + const char *mem_path, Error **errp);
> RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
> - bool share, int fd,
> + bool share, OnOffAuto sync, int fd,
> Error **errp);
> RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
> MemoryRegion *mr, Error **errp);
> diff --git a/memory.c b/memory.c
> index 449a1429b9..e22f51394e 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1572,6 +1572,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
> uint64_t size,
> uint64_t align,
> bool share,
> + OnOffAuto sync,
> const char *path,
> Error **errp)
> {
> @@ -1580,7 +1581,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
> mr->terminates = true;
> mr->destructor = memory_region_destructor_ram;
> mr->align = align;
> - mr->ram_block = qemu_ram_alloc_from_file(size, mr, share, path, errp);
> + mr->ram_block = qemu_ram_alloc_from_file(size, mr, share, sync, path, errp);
> mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
> }
>
> @@ -1596,7 +1597,8 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
> mr->ram = true;
> mr->terminates = true;
> mr->destructor = memory_region_destructor_ram;
> - mr->ram_block = qemu_ram_alloc_from_fd(size, mr, share, fd, errp);
> + mr->ram_block = qemu_ram_alloc_from_fd(size, mr, share, ON_OFF_AUTO_OFF, fd,
> + errp);
> mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
> }
> #endif
> diff --git a/numa.c b/numa.c
> index 83675a03f3..93180510a4 100644
> --- a/numa.c
> +++ b/numa.c
> @@ -457,7 +457,7 @@ static void allocate_system_memory_nonnuma(MemoryRegion *mr, Object *owner,
> #ifdef __linux__
> Error *err = NULL;
> memory_region_init_ram_from_file(mr, owner, name, ram_size, 0, false,
> - mem_path, &err);
> + ON_OFF_AUTO_OFF, mem_path, &err);
> if (err) {
> error_report_err(err);
> if (mem_prealloc) {
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 5ff741a4af..3ee423e6a8 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -3974,7 +3974,7 @@ property must be set. These objects are placed in the
>
> @table @option
>
> -@item -object memory-backend-file,id=@var{id},size=@var{size},mem-path=@var{dir},share=@var{on|off},discard-data=@var{on|off},merge=@var{on|off},dump=@var{on|off},prealloc=@var{on|off},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave},align=@var{align}
> +@item -object memory-backend-file,id=@var{id},size=@var{size},mem-path=@var{dir},share=@var{on|off},discard-data=@var{on|off},merge=@var{on|off},dump=@var{on|off},prealloc=@var{on|off},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave},align=@var{align},sync=@var{on|off|auto}
>
> Creates a memory file backend object, which can be used to back
> the guest RAM with huge pages.
> @@ -4034,6 +4034,25 @@ requires an alignment different than the default one used by QEMU, eg
> the device DAX /dev/dax0.0 requires 2M alignment rather than 4K. In
> such cases, users can specify the required alignment via this option.
>
> +The @option{sync} option specifies whether QEMU mmap(2) @option{mem-path}
> +with MAP_SYNC flag, which can fully guarantee the guest write
> +persistence to @option{mem-path}. MAP_SYNC requires supports from both
> +the host kernel (since Linux kernel 4.15) and @option{mem-path} (only
> +files supporting DAX). It can take one of following values:
> +
> +@table @option
> +@item @var{on}
> +try to pass MAP_SYNC to mmap(2); if MAP_SYNC is not supported or
> +@option{share}=@var{off}, QEMU will abort
> +
> +@item @var{off}
> +never pass MAP_SYNC to mmap(2)
> +
> +@item @var{auto} (default)
> +if MAP_SYNC is supported and @option{share}=@var{on}, work as if
> +@option{sync}=@var{on}; otherwise, work as if @option{sync}=@var{off}
> +@end table
> +
> @item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave}
>
> Creates a memory backend object, which can be used to back the guest RAM.
> --
> 2.15.1
>
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
On 01/11/18 20:06 +0000, Dr. David Alan Gilbert wrote:
> * Haozhong Zhang (haozhong.zhang@intel.com) wrote:
> > This option controls whether QEMU mmap(2) the memory backend file with
> > MAP_SYNC flag, which can fully guarantee the guest write persistence
> > to the backend, if MAP_SYNC flag is supported by the host kernel
> > (Linux kernel 4.15 and later) and the backend is a file supporting
> > DAX (e.g., file on ext4/xfs file system mounted with '-o dax').
> >
> > It can take one of following values:
> > - on: try to pass MAP_SYNC to mmap(2); if MAP_SYNC is not supported or
> > 'share=off', QEMU will abort
> > - off: never pass MAP_SYNC to mmap(2)
> > - auto (default): if MAP_SYNC is supported and 'share=on', work as if
> > 'sync=on'; otherwise, work as if 'sync=off'
>
> I don't know anything about MAP_SYNC but see two minor comments below:
>
> > Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> > Sugguested-by: Eduardo Habkost <ehabkost@redhat.com>
> ^ typo!
>
[..]
> > +static void file_memory_backend_set_sync(
> > + Object *obj, Visitor *v, const char *name, void *opaque, Error **errp)
> > +{
> > + HostMemoryBackend *backend = MEMORY_BACKEND(obj);
> > + HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
> > + Error *local_err = NULL;
> > + OnOffAuto value;
> > +
> > + if (host_memory_backend_mr_inited(backend)) {
> > + error_setg(&local_err, "cannot change property value");
>
> Please make this error clearer; if I was helping someone and saw
> this error message in a log, I wouldn't know what type of property it
> was on what device. Please at least include something saying it's
> memory backend related and sync related; even just including a %s and
> __func__ would help; even better if you include the name of the object
> so if you had multiple backend files and one failed you could see which
> one.
I'll fix the typo, and include the backend id and the property name in
the error messages in the next version.
Thanks,
Haozhong
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