Changes since v2 [1]: * Add a comment for the vma_is_fsdax() check in get_vaddr_frames() (Jan) * Collect Jan's Reviewed-by. * Rebased on v4.15-rc1 [1]: https://lists.01.org/pipermail/linux-nvdimm/2017-November/013295.html The summary text below is unchanged from v2. --- Andrew, Here is a new get_user_pages api for cases where a driver intends to keep an elevated page count indefinitely. This is distinct from usages like iov_iter_get_pages where the elevated page counts are transient. The iov_iter_get_pages cases immediately turn around and submit the pages to a device driver which will put_page when the i/o operation completes (under kernel control). In the longterm case userspace is responsible for dropping the page reference at some undefined point in the future. This is untenable for filesystem-dax case where the filesystem is in control of the lifetime of the block / page and needs reasonable limits on how long it can wait for pages in a mapping to become idle. Fixing filesystems to actually wait for dax pages to be idle before blocks from a truncate/hole-punch operation are repurposed is saved for a later patch series. Also, allowing longterm registration of dax mappings is a future patch series that introduces a "map with lease" semantic where the kernel can revoke a lease and force userspace to drop its page references. I have also tagged these for -stable to purposely break cases that might assume that longterm memory registrations for filesystem-dax mappings were supported by the kernel. The behavior regression this policy change implies is one of the reasons we maintain the "dax enabled. Warning: EXPERIMENTAL, use at your own risk" notification when mounting a filesystem in dax mode. It is worth noting the device-dax interface does not suffer the same constraints since it does not support file space management operations like hole-punch. --- Dan Williams (4): mm: introduce get_user_pages_longterm mm: fail get_vaddr_frames() for filesystem-dax mappings [media] v4l2: disable filesystem-dax mapping support IB/core: disable memory registration of fileystem-dax vmas drivers/infiniband/core/umem.c | 2 - drivers/media/v4l2-core/videobuf-dma-sg.c | 5 +- include/linux/fs.h | 14 ++++++ include/linux/mm.h | 13 ++++++ mm/frame_vector.c | 12 +++++ mm/gup.c | 64 +++++++++++++++++++++++++++++ 6 files changed, 107 insertions(+), 3 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
