From 119906afa5ca610adb87c55ab0d8e53c9104bfc3 Mon Sep 17 00:00:00 2001 From: Zhang Yi Date: Mon, 22 Apr 2019 08:48:48 +0800 Subject: util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap() When a file supporting DAX is used as vNVDIMM backend, mmap it with MAP_SYNC flag in addition which can ensure file system metadata synced in each guest writes to the backend file, without other QEMU actions (e.g., periodic fsync() by QEMU). Current, We have below different possible use cases: 1. pmem=on is set, shared=on is set, MAP_SYNC supported: a: backend is a dax supporting file. - MAP_SYNC will active. b: backend is not a dax supporting file. - mmap will trigger a warning. then MAP_SYNC flag will be ignored 2. The rest of cases: - we will never pass the MAP_SYNC to mmap2 Signed-off-by: Haozhong Zhang Signed-off-by: Zhang Yi [ehabkost: Rebased patch to latest code on master] Signed-off-by: Eduardo Habkost Signed-off-by: Wei Yang Tested-by: Wei Yang Message-Id: <20190422004849.26463-2-richardw.yang@linux.intel.com> [ehabkost: squashed documentation patch] Message-Id: <20190422004849.26463-3-richardw.yang@linux.intel.com> [ehabkost: documentation fixup] Reviewed-by: Michael S. Tsirkin Reviewed-by: Pankaj Gupta Reviewed-by: Stefan Hajnoczi Signed-off-by: Eduardo Habkost --- qemu-options.hx | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'qemu-options.hx') diff --git a/qemu-options.hx b/qemu-options.hx index 08749a3391..bdc74c0620 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4233,6 +4233,11 @@ using the SNIA NVM programming model (e.g. Intel NVDIMM). If @option{pmem} is set to 'on', QEMU will take necessary operations to guarantee the persistence of its own writes to @option{mem-path} (e.g. in vNVDIMM label emulation and live migration). +Also, we will map the backend-file with MAP_SYNC flag, which ensures the +file metadata is in sync for @option{mem-path} in case of host crash +or a power failure. MAP_SYNC requires support from both the host kernel +(since Linux kernel 4.15) and the filesystem of @option{mem-path} mounted +with DAX option. @item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave} -- cgit 1.4.1