On Wed, Jul 10, 2019 at 10:26:47PM +0200, Jan Kara wrote:
On Wed 10-07-19 13:15:39, Matthew Wilcox wrote:
On Wed, Jul 10, 2019 at 09:02:04PM +0200, Jan Kara wrote:
+#define DAX_ENTRY_CONFLICT dax_make_entry(pfn_to_pfn_t(1), DAX_EMPTY)
I was hoping to get rid of DAX_EMPTY ... it's almost unused now. Once we switch to having a single DAX_LOCK value instead of a single bit, I think it can go away, freeing up two bits.
If you really want a special DAX_ENTRY_CONFLICT, I think we can make one in the 2..4094 range.
That aside, this looks pretty similar to the previous patch I sent, so if you're now happy with this, let's add
#define XA_DAX_CONFLICT_ENTRY xa_mk_internal(258)
to xarray.h and do it that way?
Yeah, that would work for me as well. The chosen value for DAX_ENTRY_CONFLICT was pretty arbitrary. Or we could possibly use:
#define DAX_ENTRY_CONFLICT XA_ZERO_ENTRY
so that we don't leak DAX-specific internal definition into xarray.h?
I don't want to use the ZERO entry as our conflict marker because that could legitimately appear in an XArray. Not the i_pages XArray today, but I hold out hope for using that in place of the DAX_ZERO_PAGE bit too. That's going to be a bit more tricky since we currently distinguish between DAX_ZERO_PAGE and DAX_ZERO_PAGE | DAX_PMD.
However, the XA_RETRY_ENTRY might be a good choice. It doesn't normally appear in an XArray (it may appear if you're looking at a deleted node, but since we're holding the lock, we can't see deleted nodes).