Re: [Qemu-devel] [PATCH v5 0/7] nvdimm: support MAP_SYNC for memory-backend-file

[Stefan Hajnoczi]

On Mon, Nov 05, 2018 at 04:07:50PM +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').
> 

Hi,
There are a lot of people on CC so probably no one felt responsible to
review this series quickly.  Feel free to send a "ping" email if your
patches aren't receiving attention.

Overall this feature looks fine.  I left a few small comments.

Thanks,
Stefan

> 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'
> 
> 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 (7):
>   numa: Fixed the memory leak of numa error message
>   util/mmap-alloc: switch qemu_ram_mmap() to 'flags' parameter
>   exec: switch qemu_ram_alloc_from_{file, fd} to the '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/standard-headers/linux/mman.h | 44 ++++++++++++++++++++++++++++++++++
>  numa.c                                |  1 +
>  qemu-options.hx                       | 22 ++++++++++++++++-
>  util/mmap-alloc.c                     | 26 ++++++++++++++++----
>  util/oslib-posix.c                    |  4 +++-
>  12 files changed, 200 insertions(+), 18 deletions(-)
>  create mode 100644 include/standard-headers/linux/mman.h
> 
> -- 
> 2.7.4
> 
>

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