On Wed 17-08-16 10:21:24, Ross Zwisler wrote: > On Mon, Aug 15, 2016 at 02:14:14PM -0700, Dan Williams wrote: > > On Mon, Aug 15, 2016 at 2:11 PM, Ross Zwisler > > <ross.zwisler@xxxxxxxxxxxxxxx> wrote: > > > On Mon, Aug 15, 2016 at 01:21:47PM -0700, Dan Williams wrote: > > >> On Mon, Aug 15, 2016 at 12:09 PM, Ross Zwisler > > >> <ross.zwisler@xxxxxxxxxxxxxxx> wrote: > > >> > DAX PMDs have been disabled since Jan Kara introduced DAX radix tree based > > >> > locking. This series allows DAX PMDs to participate in the DAX radix tree > > >> > based locking scheme so that they can be re-enabled. > > >> > > >> Looks good to me. > > >> > > >> > This series restores DAX PMD functionality back to what it was before it > > >> > was disabled. There is still a known issue between DAX PMDs and hole > > >> > punch, which I am currently working on and which I plan to address with a > > >> > separate series. > > >> > > >> Perhaps we should hold off on applying patch 6 and 7 until after the > > >> hole-punch fix is ready? > > > > > > Sure, I'm cool with holding off on patch 7 (the Kconfig change) until after > > > the hole punch fix is ready. > > > > > > I don't see a reason to hold off on patch 6, though? It stands on it's own, > > > implements the correct locking, and doesn't break anything. > > > > Whoops, I just meant 7. > > Well, it looks like the hole punch case is much improved since I tested it > last! :) I used to be able to generate a few different kernel BUGs when hole > punching DAX PMDs, but those have apparently been fixed in the mm layer since > I was last testing, which admittedly was quite a long time ago (February?). > > The only issue I was able to find with DAX PMD hole punching was that ext4 > wasn't properly doing a writeback before the hole was unmapped and the radix > tree entries were removed. This issue applies equally to the 4k case, so I've > submitted a bug fix for v4.8: > > https://lists.01.org/pipermail/linux-nvdimm/2016-August/006621.html > > With that applied, I don't know of any more issues related to DAX PMDs and > hole punch. I've tested ext4 and XFS (ext2 doesn't support hole punch), and > they both properly do a writeback of all affected PMDs, fully unmap all > affected PMDs, and remove the radix tree entries. I've tested that new page > faults for addresses previously covered by the old PMDs generate new page > faults, and 4k pages are now faulted in because the block allocator no longer > has 2MiB contiguous allocations. > > One question (probably for Jan): should the above ext4 fix be marked for > stable? Yes, probably it should be. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
