> -----Original Message----- > From: Linux-nvdimm [mailto:linux-nvdimm-bounces@xxxxxxxxxxxx] On Behalf Of > Jan Kara > Sent: Wednesday, October 21, 2015 4:08 AM ... > On Tue 20-10-15 17:31:18, Dan Williams wrote: > > On Tue, Oct 20, 2015 at 5:01 PM, Dave Chinner <david@xxxxxxxxxxxxx> ... > > I'm wondering if we can take a conservative step forward with those > > patches for 4.4. if XFS and EXT4 interactions need more time to get > > worked out, which I believe they do, I can conceive just turning on > > get_user_pages() support for DAX-mappings of the raw block device. > > This would be via the new facility I posted yesterday: > > https://lists.01.org/pipermail/linux-nvdimm/2015-October/002512.html. > > While not very functional for applications it makes testing base DAX > > mechanisms straightforward. > > I had a look at the patch and I miss one thing: Why do we need bd_mutex > to protect faults? I see a comment there: > > /* check that the faulting page hasn't raced with bdev resize */ > > Is it really possible that bdev gets shrunk under us? Hum, looking into > fs/block_dev.c, probably it is. But there are other places - like DIO path > - assuming that block device mapping cannot just disappear from under us. > I wonder how that would cope with bdev size change... DIO_IGNORE_TRUNCATE was added to eliminate an awful lot of CPU time incrementing and decrementing i_dio_count for direct IO to block devices, especially at pmem type speeds. I hope that kind of accounting doesn't need to be brought back. https://lkml.org/lkml/2015/4/3/557 https://lkml.org/lkml/2015/4/15/590 --- Robert Elliott, HPE Persistent Memory -- 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
