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[Qemu-devel] [PATCH V8 0/5] support MAP_SYNC for memory-backend-file

From: Zhang Yi
Subject: [Qemu-devel] [PATCH V8 0/5] support MAP_SYNC for memory-backend-file
Date: Wed, 2 Jan 2019 13:25:21 +0800

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

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 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' or 'pmem=off', QEMU will not pass this flag to mmap(2)
 - off: (default) never pass MAP_SYNC to mmap(2)

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 
   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

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):
  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()
  hostmem: add more information in error messages
  hostmem-file: add 'sync' option

 backends/hostmem-file.c   | 34 ++++++++++++++++++++++++++++++++--
 backends/hostmem.c        |  8 +++++---
 docs/nvdimm.txt           | 23 ++++++++++++++++++++++-
 exec.c                    |  9 +++++----
 include/exec/memory.h     | 26 ++++++++++++++++++++------
 include/exec/ram_addr.h   |  1 +
 include/qemu/mmap-alloc.h | 20 +++++++++++++++++++-
 include/qemu/osdep.h      | 16 ++++++++++++++++
 numa.c                    |  1 +
 qemu-options.hx           | 19 ++++++++++++++++++-
 util/mmap-alloc.c         | 20 ++++++++++++++++----
 util/oslib-posix.c        |  9 ++++++++-
 12 files changed, 163 insertions(+), 23 deletions(-)


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