Re: [Qemu-devel] [PATCH V10 0/4] support MAP_SYNC for memory-backend-file

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jan 23, 2019 at 10:59:27AM +0800, Zhang, Yi wrote:
> From: "Zhang,Yi" <yi.z.zhang@linux.intel.com>
> 
> 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)

How was this patch tested? Given the previous version apparently
passed the combination of flags ignored by Linux,
enquiring minds want to know.

> Changes in V10:
>  * 4/4: refine the document.
>  * 3/4: Reviewed-by: Stefano Garzarella <sgarzare@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 <ehabkost@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 (4):
>   util/mmap-alloc: switch 'shared' to 'flags' parameter
>   util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap()
>   hostmem: add more information in error messages
>   docs: Added MAP_SYNC documentation
> 
>  backends/hostmem-file.c   |  6 ++++--
>  backends/hostmem.c        |  8 +++++---
>  docs/nvdimm.txt           | 29 ++++++++++++++++++++++++++++-
>  exec.c                    |  7 ++++---
>  include/qemu/mmap-alloc.h | 20 +++++++++++++++++++-
>  include/qemu/osdep.h      | 21 +++++++++++++++++++++
>  qemu-options.hx           |  4 ++++
>  util/mmap-alloc.c         | 15 +++++++++++----
>  util/oslib-posix.c        |  9 ++++++++-
>  9 files changed, 104 insertions(+), 15 deletions(-)
> 
> -- 
> 2.7.4