On Wed, Oct 21, 2015 at 3:36 PM, Elliott, Robert (Persistent Memory) <elliott@xxxxxxx> wrote: > > >> -----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 Thanks for that reminder Robert. I think this backs up my suspicion that the base mmap_sem protections should be enough for raw block mmap + DAX. -- 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
