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From: Jingqi Liu <jingqi.liu@intel.com>
To: Stefan Hajnoczi <stefanha@redhat.com>,
	Pankaj Gupta <pankaj.gupta.linux@gmail.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Xiao Guangrong <xiaoguangrong.eric@gmail.com>,
	Dan Williams <dan.j.williams@intel.com>
Cc: Jingqi Liu <jingqi.liu@intel.com>, qemu-devel@nongnu.org
Subject: [PATCH] docs/nvdimm: add 'pmem=on' for the device dax backend file
Date: Mon,  3 Aug 2020 08:35:18 +0800	[thread overview]
Message-ID: <20200803003518.88891-1-jingqi.liu@intel.com> (raw)

At the end of live migration, QEMU uses msync() to flush the data to
the backend storage. When the backend file is a character device dax,
the pages explicitly avoid the page cache. It will return failure from msync().
The following warning is output.

    "warning: qemu_ram_msync: failed to sync memory range“

So we add 'pmem=on' to avoid calling msync(), use the QEMU command line:

    -object memory-backend-file,id=mem1,pmem=on,mem-path=/dev/dax0.0,size=4G

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
---
 docs/nvdimm.txt | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
index c2c6e441b3..31048aff5e 100644
--- a/docs/nvdimm.txt
+++ b/docs/nvdimm.txt
@@ -243,6 +243,13 @@ use the QEMU command line:
 
     -object memory-backend-file,id=nv_mem,mem-path=/XXX/yyy,size=4G,pmem=on
 
+At the end of live migration, QEMU uses msync() to flush the data to the
+backend storage. When the backend file is a character device dax, the pages
+explicitly avoid the page cache. It will return failure from msync().
+So we add 'pmem=on' to avoid calling msync(), use the QEMU command line:
+
+    -object memory-backend-file,id=mem1,pmem=on,mem-path=/dev/dax0.0,size=4G
+
 References
 ----------
 
-- 
2.17.1



             reply	other threads:[~2020-08-03  0:46 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-03  0:35 Jingqi Liu [this message]
  -- strict thread matches above, loose matches on Subject: below --
2020-07-30  1:02 [PATCH] docs/nvdimm: add 'pmem=on' for the device dax backend file Jingqi Liu
2020-07-30  5:07 ` Pankaj Gupta
2020-07-15  2:54 Jingqi Liu
2020-07-24  7:15 ` Liu, Jingqi
2020-07-28  1:09 ` Liu, Jingqi
2020-07-29 10:42 ` Stefan Hajnoczi

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