On Sun, Jan 31, 2016 at 10:18:46AM -0800, Dan Williams wrote: > On Sun, Jan 31, 2016 at 10:07 AM, Matthew Wilcox <wi...@linux.intel.com> > wrote: > > Yes. This is just the default implementation of dax_map_pfn() which works > > for most situations. We can introduce more complex implementations of > > dax_map_pfn() as necessary. You make another excellent point for why > > we should store PFNs in the radix tree instead of kaddrs :-) > > How much complexity do we want to add in support of an fsync/msync > mechanism that is not the recommended way to use DAX?
It actually makes the dax_io path much, much simpler. And it's not primarily about fixing fsync/msync. It also makes the fault path cheaper in the case where we're refaulting a page that's already been faulted by another process (or was previously faulted by this process and now needs to be faulted at a different address). And it fixes the problem with filesystems that use multiple block_devices. It also makes DAX much less reliant on buffer heads, which is good for the problem that Jared raised where he doesn't have a block_device in an embedded system.
