On Sun, Jan 31, 2016 at 10:27 AM, Matthew Wilcox <wi...@linux.intel.com> wrote: > 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.
Oh I thought we were talking about what goes in the radix. Sure, de-emphasizing the usage of a block_device throughout the dax implementation is interesting. It also has some synergy with the LSF/MM topic I'm writing up "pmem as storage device vs pmem as memory".
