On Mon, Apr 22, 2019 at 08:34:51AM -0400, Michael S. Tsirkin wrote: > On Mon, Apr 22, 2019 at 08:48:47AM +0800, Wei Yang wrote: > > 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) > > OK this is in a good shape. As we are in freeze anyway, > there's still a bit more time to polish it. I have a couple of > suggestions: > > - squash docs in same patch with code, no need for two patches > - mmap errors are not silently ignored as the doc says, > a warning is produced
Note that a warning is produced only if both share=on and pmem=on is specified. If using pmem=on without share=on, no warning is printed at all. I agree we could squash the docs in the same patch, but I don't want to prevent the code from being merged and require v15 to be sent just because we are still polishing the documentation. If there are no objections, I plan to apply this version of the series including the following fixup (just removing the word "silently"), and I suggest further improvements to be sent as follow up patches. diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt index bcd1456e72..b531cacd35 100644 --- a/docs/nvdimm.txt +++ b/docs/nvdimm.txt @@ -159,8 +159,8 @@ If these conditions are not satisfied i.e. if either 'pmem' or 'share' are not set, if the backend file does not support DAX or if MAP_SYNC is not supported by the host kernel, write persistence is not guaranteed after a system crash. For compatibility reasons, these -conditions are silently ignored if not satisfied. Currently, no way -is provided to test for them. +conditions are ignored if not satisfied. Currently, no way is +provided to test for them. For more details, please reference mmap(2) man page: http://man7.org/linux/man-pages/man2/mmap.2.html. -- Eduardo
