Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs
Dan Williams <[email protected]> Thu, 15 Sep 2016 10:01:03 -0700
| Newsgroups | gmane.comp.file-systems.xfs.general |
|---|---|
| Message-ID | <CAPcyv4jTw3cXpmmJRh7t16Xy2uYofDe+fJ+X_jnz+Q=o0uGneg__9529.3860919357$1473958885$gmane$org@mail.gmail.com> |
On Thu, Sep 15, 2016 at 1:26 AM, Christoph Hellwig <[email protected]> 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. _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs