On Thu, Sep 15, 2016 at 1:26 AM, Christoph Hellwig <hch@xxxxxx> wrote: > On Wed, Sep 14, 2016 at 11:54:38PM -0700, Dan Williams wrote: >> The DAX property, page cache bypass, of a VMA is only detectable via the >> vma_is_dax() helper to check the S_DAX inode flag. However, this is >> only available internal to the kernel and is a property that userspace >> applications would like to interrogate. > > They have absolutely no business knowing such an implementation detail. Hasn't that train already left the station with FS_XFLAG_DAX? The other problem with hiding the DAX property is that it turns out to not be a transparent acceleration feature. See xfs/086 xfs/088 xfs/089 xfs/091 which fail with DAX and, as far as I understand, it is due to the fact that DAX disallows delayed allocation behavior. If behavior changes I think we should indicate that to userspace and VM_DAX is certainly more useful to userspace than some of the other vm internals we already export in those flags. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>