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

[Yi Zhang <yi.z.zhang@linux.intel.com>]

On 2019-01-22 at 22:01:58 -0500, Michael S. Tsirkin wrote:
> 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.
Ah. Sorry, We Have missed the flag MAP_SHARED_VALIDATE in V9, V8 and previous
are tested. already fixed in the 2/4.
> 
> > 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