Linux 4.15 introduces a new mmap flag MAP_SYNC, which can be used to
guarantee the write persistence to mmap'ed files supporting DAX (e.g.,
files on ext4/xfs file system mounted with '-o dax').
A description of MAP_SYNC and MAP_SHARED_VALIDATE can be found at
https://patchwork.kernel.org/patch/10028151/
In order to make sure that the file metadata is in sync after a fault
while we are writing a shared DAX supporting backend files, this
patch-set enables QEMU to use MAP_SYNC flag for memory-backend-dax-file.
As the DAX vs DMA truncated issue was solved, we refined the code and
send out this feature for the v5 version.
We will pass MAP_SYNC to mmap(2); if MAP_SYNC is supported and
'share=on' & 'pmem=on'.
Or QEMU will not pass this flag to mmap(2)
Test with below cases:
1. pmem=on is set, shared=on is set, MAP_SYNC supported:
a: backend is a dax supporting file.
1) start VM1 with options:
-object
memory-backend-file,id=nv_be4,share,mem-path=${DAX_FILE_1},size=${DAX_FILE_SIZE_1},align=128M,pmem=on,share=on
-device nvdimm,id=nv4,memdev=nv_be4,label-size=2M.
2) start VM2 with options:
-object
memory-backend-file,id=nv_be4,share,mem-path=${DAX_FILE_2,size=${DAX_FILE_SIZE_2},align=128M,pmem=on,share=on
-device nvdimm,id=nv4,memdev=nv_be4,label-size=2M.
3) live migrate from VM1 to VM2.
4) Suddly let Host crash or power failure.
5) check DAX_FILE_1 and DAX_FILE_2, no corrupt.
b: backend is a regular file.
1) start with options
-object
memory-backend-file,id=nv_be4,share,mem-path=${REG_FILE},size=${REG_FILE_SIZE},align=128M,pmem=on,share=on
-device nvdimm,id=nv4,memdev=nv_be4,label-size=2M.
will warning "failed to validate with mapping flags: Operation not supported"
FILE_1 and FILE_2 random corrupt.
2. Other cases:
FILE_1 and FILE_2 random corrupt.
Changes in V12:
* 2/5: Micheal: Update update-linux-headers.sh
* 3/5: Micheal: Use script update add linux/mman.h
* 4/5: Pankaj,Micheal: 1) fallback to mmap without
MAP_SYNC & MAP_SHARED_VALIDATE if sync not supported or failed
2) Replace the include with 3/5 added linux/mman.h
* 5/5: Micheal: Refine the Documentations.
Changes in V11:
* 1/3: Micheal: Change to just add a bool is_pmem in qemu_ram_mmap.
* 2/3: Micheal: Fix the compatibility for old kernel.
* 2/3&3/3: Micheal&Eduardo :Update the behavior below:
Waning at no-dax and continue without MAP_SYNC.
Test if fails again for compatibility, then remove the MAP_VALIDATE and
silently proceed.
Changes in V10:
* 4/4: refine the document.
* 3/4: Reviewed-by: Stefano Garzarella <sgarz...@redhat.com>
* 2/4: refine the commit message, Added MAP_SHARED_VALIDATE.
* 2/4: Fix the wrong include header
Changes in V9:
* 1/6: Reviewed-by: Eduardo Habkost <ehabk...@redhat.com>
* 2/6: New Added: Micheal: use sparse feature define RAM_FLAG.
since I don't have much knowledge about the sparse feature, @Micheal Could you
add some documentation/commit message on this patch? Thank you very much.
* 3/6: from 2/5: Eduardo: updated the commit message.
* 4/6: from 3/5: Micheal: don't ignore MAP_SYNC failures silently.
* 5/6: from 4/5: Eduardo: updated the commit message.
* 6/6: from 5/5: Micheal: Drop the sync option, document the MAP_SYNC.
Changes in v8:
* Micheal: 3/5, remove the duplicated define in the os_dep.h
* Micheal: 2/5, make type define safety.
* Micheal: 2/5, fixed the incorrect define MAP_SHARE on qemu_anon_ram_alloc.
* 4/6 removed, we remove the on/off/auto define of sync, as by now,
MAP_SYNC only worked with pmem=on.
* @Micheal, I still reuse the RAM_SYNC flag, it is much straightforward to
parse
all the flags in one parameter.
Changes in v7:
* Micheal: [3,4,6]/6 limited the "sync" flag only on a nvdimm backend.(pmem=on)
Changes in v6:
* Pankaj: 3/7 are squashed with 2/7
* Pankaj: 7/7 update comments to "consistent filesystem metadata".
* Pankaj, Igor: 1/7 Added Reviewed-by in patch-1/7
* Stefan, 4/7 move the include header from "/linux/mman.h" to "osdep.h"
* Stefan, 5/7 Add missing "munmap"
* Stefan, 2/7 refine the shared/flag.
Changes in v5:
* Add patch 1 to fix a memory leak issue.
* Refine the patch 4-6
* Remove the patch 3 as we already change the parameter from "shared" to
"flags"
Changes in v4:
* Add patch 1-3 to switch some functions to a single 'flags'
parameters. (Michael S. Tsirkin)
* v3 patch 1-3 become v4 patch 4-6.
* Patch 4: move definitions of MAP_SYNC and MAP_SHARED_VALIDATE to a
new header file under include/standard-headers/linux/. (Michael S. Tsirkin)
* Patch 6: refine the description of the 'sync' option. (Michael S. Tsirkin)
Changes in v3:
* Patch 1: add MAP_SHARED_VALIDATE in both sync=on and sync=auto
cases, and add back the retry mechanism. MAP_SYNC will be ignored
by Linux kernel 4.15 if MAP_SHARED_VALIDATE is missed.
* Patch 1: define MAP_SYNC and MAP_SHARED_VALIDATE as 0 on non-Linux
platforms in order to make qemu_ram_mmap() compile on those platforms.
* Patch 2&3: include more information in error messages of
memory-backend in hope to help user to identify the error.
(Dr. David Alan Gilbert)
* Patch 3: fix typo in the commit message. (Dr. David Alan Gilbert)
Changes in v2:
* Add 'sync' option to control the use of MAP_SYNC. (Eduardo Habkost)
* Remove the unnecessary set of MAP_SHARED_VALIDATE in some cases and
the retry mechanism in qemu_ram_mmap(). (Michael S. Tsirkin)
* Move OS dependent definitions of MAP_SYNC and MAP_SHARED_VALIDATE
to osdep.h. (Michael S. Tsirkin)
Zhang Yi (5):
util/mmap-alloc: Add a 'is_pmem' parameter to qemu_ram_mmap
scripts/update-linux-headers: add linux/mman.h
linux-headers: add linux/mman.h.
util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap()
docs: Added MAP_SYNC documentation
docs/nvdimm.txt | 25 ++++++-
exec.c | 2 +-
include/qemu/mmap-alloc.h | 21 +++++-
include/qemu/osdep.h | 7 ++
linux-headers/asm-arm/mman.h | 4 ++
linux-headers/asm-arm64/mman.h | 1 +
linux-headers/asm-generic/hugetlb_encode.h | 36 ++++++++++
linux-headers/asm-generic/mman-common.h | 77 ++++++++++++++++++++
linux-headers/asm-generic/mman.h | 24 +++++++
linux-headers/asm-mips/mman.h | 108 +++++++++++++++++++++++++++++
linux-headers/asm-powerpc/mman.h | 39 +++++++++++
linux-headers/asm-s390/mman.h | 1 +
linux-headers/asm-x86/mman.h | 31 +++++++++
linux-headers/linux/mman.h | 38 ++++++++++
qemu-options.hx | 4 ++
scripts/update-linux-headers.sh | 6 +-
util/mmap-alloc.c | 30 +++++++-
util/oslib-posix.c | 2 +-
18 files changed, 445 insertions(+), 11 deletions(-)
create mode 100644 linux-headers/asm-arm/mman.h
create mode 100644 linux-headers/asm-arm64/mman.h
create mode 100644 linux-headers/asm-generic/hugetlb_encode.h
create mode 100644 linux-headers/asm-generic/mman-common.h
create mode 100644 linux-headers/asm-generic/mman.h
create mode 100644 linux-headers/asm-mips/mman.h
create mode 100644 linux-headers/asm-powerpc/mman.h
create mode 100644 linux-headers/asm-s390/mman.h
create mode 100644 linux-headers/asm-x86/mman.h
create mode 100644 linux-headers/linux/mman.h
--
2.7.4
