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Re: [Qemu-devel] [PATCH v3 3/3] hostmem-file: add 'sync' option
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v3 3/3] hostmem-file: add 'sync' option |
Date: |
Wed, 24 Jan 2018 22:23:35 +0200 |
On Wed, Jan 17, 2018 at 04:13:25PM +0800, Haozhong Zhang 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'
>
> Signed-off-by: Haozhong Zhang <address@hidden>
> Suggested-by: Eduardo Habkost <address@hidden>
> ---
> backends/hostmem-file.c | 40 +++++++++++++++++++++++++++++++++++++++-
> 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, 93 insertions(+), 14 deletions(-)
>
> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> index ed7d145365..96dff38619 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
> @@ -153,6 +155,39 @@ 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 '%s' of %s '%s'",
> + name, object_get_typename(obj), backend->id);
> + 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);
> @@ -187,6 +222,9 @@ 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}.
I would add ... even in case of a host power loss.
Here and wherever you say "fully".
> 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.
> --
> 2.14.1