On Mon, Dec 17, 2018 at 01:53:54PM +0800, Yi Zhang wrote: > On 2018-12-12 at 10:06:13 -0500, Michael S. Tsirkin wrote: > > On Wed, Dec 12, 2018 at 04:11:44PM +0800, Zhang Yi wrote: > > > 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. > > > > > > A new auto on/off option 'sync' is added to memory-backend-file: > > > - 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' > > > > Can this change be limited to a real DAX device? > > Then you won't need to bother with flags at all. > Thanks Micheal's review, > > For real dax device, we still need to have a option to turn sync off.
Not sure why really. Why use an nvdimm if you don't actually want it to be persistent? > > > > And am I mistaken in thinking that this will affect all > > guest memory with share=on? Or do I misunderstand? > > Only file-backend memory with share=on. Yes but that's everyone if e.g. vhost-user needs to be active. So frankly I don't think it's a good idea to change the default like this unless it's limited to nvdimm in some way. > > > > > > > > > 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 (6): > > > numa: Fixed the memory leak of numa error message > > > util/mmap-alloc: switch qemu_ram_mmap() to 'flags' parameter > > > util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap() > > > util/mmap-alloc: Switch the RAM_SYNC flags to OnOffAuto > > > hostmem: add more information in error messages > > > hostmem-file: add 'sync' option > > > > > > backends/hostmem-file.c | 45 > > > +++++++++++++++++++++++++++++++++++++++++++-- > > > backends/hostmem.c | 8 +++++--- > > > docs/nvdimm.txt | 20 +++++++++++++++++++- > > > exec.c | 9 +++++---- > > > include/exec/memory.h | 18 ++++++++++++++++++ > > > include/exec/ram_addr.h | 1 + > > > include/qemu/mmap-alloc.h | 20 +++++++++++++++++++- > > > include/qemu/osdep.h | 29 +++++++++++++++++++++++++++++ > > > numa.c | 1 + > > > qemu-options.hx | 22 +++++++++++++++++++++- > > > util/mmap-alloc.c | 26 +++++++++++++++++++++----- > > > util/oslib-posix.c | 8 +++++++- > > > 12 files changed, 189 insertions(+), 18 deletions(-) > > > > > > -- > > > 2.7.4
