Re: [Qemu-devel] [PATCH V6 0/7] nvdimm: guarantee persistence of QEMU writes to persistent memory

[Junyan He]

He have pmem_persist and pmem_memcpy_persist stub functions.

If no libpmem and user really specify pmem=on, we just do nothing or just 
memcpy.

Real persistent memory always require libpmem support its load/save.

If pmem=on and without libpmem, we can think that user want to imitate

pmem=on while the HW environment is without real persistent memory existing.

It may help debug on some machine without real pmem.

________________________________
From: Qemu-devel <address@hidden> on behalf of Igor Mammedov <address@hidden>
Sent: Tuesday, June 12, 2018 12:06:43 PM
To: address@hidden
Cc: Haozhong Zhang; address@hidden; address@hidden; address@hidden; 
address@hidden; address@hidden; address@hidden; Junyan He; address@hidden; 
address@hidden; address@hidden; address@hidden
Subject: Re: [Qemu-devel] [PATCH V6 0/7] nvdimm: guarantee persistence of QEMU 
writes to persistent memory

On Fri,  1 Jun 2018 16:10:22 +0800
address@hidden wrote:

> From: Junyan He <address@hidden>
>
> QEMU writes to vNVDIMM backends in the vNVDIMM label emulation and
> live migration. If the backend is on the persistent memory, QEMU needs
> to take proper operations to ensure its writes persistent on the
> persistent memory. Otherwise, a host power failure may result in the
> loss the guest data on the persistent memory.

extra question, what are expected behavior when QEMU is built without
libpmem and user specifies pmem=on for backend?

>
> This v3 patch series is based on Marcel's patch "mem: add share
> parameter to memory-backend-ram" [1] because of the changes in patch 1.
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg03858.html
>
> Previous versions can be found at
> v5: https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg02258.html
> V4: https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg06993.html
> v3: https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg04365.html
> v2: https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg01579.html
> v1: https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg05040.html
>
> Changes in v6:
> * (Patch 1) Expose all ram block flags rather than redefine the flags.
> * (Patch 4) Use pkg-config rather the hard check when configure.
> * (Patch 7) Sync and flush all the pmem data when migration completes,
> rather than sync pages one by one in previous version.
>
> Changes in v5:
> * (Patch 9) Add post copy check and output some messages for nvdimm.
>
> Changes in v4:
> * (Patch 2) Fix compilation errors found by patchew.
>
> Changes in v3:
> * (Patch 5) Add a is_pmem flag to ram_handle_compressed() and handle
> PMEM writes in it, so we don't need the _common function.
> * (Patch 6) Expose qemu_get_buffer_common so we can remove the
> unnecessary qemu_get_buffer_to_pmem wrapper.
> * (Patch 8) Add a is_pmem flag to xbzrle_decode_buffer() and handle
> PMEM writes in it, so we can remove the unnecessary
> xbzrle_decode_buffer_{common, to_pmem}.
> * Move libpmem stubs to stubs/pmem.c and fix the compilation failures
> of test-{xbzrle,vmstate}.c.
>
> Changes in v2:
> * (Patch 1) Use a flags parameter in file ram allocation functions.
> * (Patch 2) Add a new option 'pmem' to hostmem-file.
> * (Patch 3) Use libpmem to operate on the persistent memory, rather
> than re-implementing those operations in QEMU.
> * (Patch 5-8) Consider the write persistence in the migration path.
>
>
> Junyan:
> [1/7] memory, exec: Expose all memory block related flags.
> [6/7] migration/ram: Add check and info message to nvdimm post copy.
> [7/7] migration/ram: ensure write persistence on loading all date to PMEM.
>
> Haozhong:
> [5/7] mem/nvdimm: ensure write persistence to PMEM in label emulation
>
> Haozhong & Junyan:
> [2/7] memory, exec: switch file ram allocation functions to 'flags' parameters
> [3/7] hostmem-file: add the 'pmem' option
> [4/7] configure: add libpmem support
>
>
> Signed-off-by: Haozhong Zhang <address@hidden>
> Signed-off-by: Junyan He <address@hidden>
>
> ---
> backends/hostmem-file.c | 28 +++++++++++++++++++++++++++-
> configure               | 29 +++++++++++++++++++++++++++++
> docs/nvdimm.txt         | 14 ++++++++++++++
> exec.c                  | 36 ++++++++++++++----------------------
> hw/mem/nvdimm.c         |  9 ++++++++-
> include/exec/memory.h   | 31 +++++++++++++++++++++++++++++--
> include/exec/ram_addr.h | 28 ++++++++++++++++++++++++++--
> include/qemu/pmem.h     | 24 ++++++++++++++++++++++++
> memory.c                |  8 +++++---
> migration/ram.c         | 18 ++++++++++++++++++
> numa.c                  |  2 +-
> qemu-options.hx         |  7 +++++++
> stubs/Makefile.objs     |  1 +
> stubs/pmem.c            | 23 +++++++++++++++++++++++
> 14 files changed, 226 insertions(+), 32 deletions(-)