On Tue, Sep 01, 2015 at 09:38:03AM +1000, Dave Chinner wrote: > On Mon, Aug 31, 2015 at 12:59:44PM -0600, Ross Zwisler wrote: > > For DAX msync we just need to flush the given range using > > wb_cache_pmem(), which is now a public part of the PMEM API. > > This is wrong, because it still leaves fsync() broken on dax. > > Flushing dirty data to stable storage is the responsibility of the > writeback infrastructure, not the VMA/mm infrasrtucture. For non-dax > configurations, msync defers all that to vfs_fsync_range(), because > it has to be implemented there for fsync() to work. > > Even for DAX, msync has to call vfs_fsync_range() for the filesystem to commit > the backing store allocations to stable storage, so there's not > getting around the fact msync is the wrong place to be flushing > DAX mappings to persistent storage. DAX does call ->fsync before and after this patch. And with all the recent fixes we take care to ensure data is written though the cache for everything but mmap-access. With this patch from Ross we ensure msync writes back the cache before calling ->fsync so that the filesystem can then do it's work like converting unwritten extents. The only downside is that previously on Linux you could always use fsync as a replaement for msymc, which isn't true anymore for DAX. But given that we need the virtual address to write back the cache I can't see how to do this differently given that clwb() needs the user virtual address to flush the cache. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
