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[Qemu-devel] [PATCH v2 2/2] hostmem-file: add 'sync' option
|
From: |
Haozhong Zhang |
|
Subject: |
[Qemu-devel] [PATCH v2 2/2] hostmem-file: add 'sync' option |
|
Date: |
Thu, 11 Jan 2018 22:22:08 +0800 |
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 <address@hidden>
Sugguested-by: Eduardo Habkost <address@hidden>
---
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
address@hidden -object
memory-backend-file,address@hidden,address@hidden,address@hidden,address@hidden|off},address@hidden|off},address@hidden|off},address@hidden|off},address@hidden|off},address@hidden,address@hidden|preferred|bind|interleave},address@hidden
address@hidden -object
memory-backend-file,address@hidden,address@hidden,address@hidden,address@hidden|off},address@hidden|off},address@hidden|off},address@hidden|off},address@hidden|off},address@hidden,address@hidden|preferred|bind|interleave},address@hidden,address@hidden|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:
+
address@hidden @option
address@hidden @var{on}
+try to pass MAP_SYNC to mmap(2); if MAP_SYNC is not supported or
address@hidden@var{off}, QEMU will abort
+
address@hidden @var{off}
+never pass MAP_SYNC to mmap(2)
+
address@hidden @var{auto} (default)
+if MAP_SYNC is supported and @address@hidden, work as if
address@hidden@var{on}; otherwise, work as if @address@hidden
address@hidden table
+
@item -object
memory-backend-ram,address@hidden,address@hidden|off},address@hidden|off},address@hidden|off},address@hidden,address@hidden,address@hidden|preferred|bind|interleave}
Creates a memory backend object, which can be used to back the guest RAM.
--
2.15.1