| From: |
| Dan Williams <dan.j.williams-AT-intel.com> |
| To: |
| akpm-AT-linux-foundation.org |
| Subject: |
| [PATCH 0/3] introduce get_user_pages_longterm() |
| Date: |
| Mon, 06 Nov 2017 16:57:10 -0800 |
| Message-ID: |
| <151001623063.16354.14661493921524115663.stgit@dwillia2-desk3.amr.corp.intel.com> |
| Cc: |
| Sean Hefty <sean.hefty-AT-intel.com>, Jan Kara <jack-AT-suse.cz>, linux-rdma-AT-vger.kernel.org, linux-kernel-AT-vger.kernel.org, Doug Ledford <dledford-AT-redhat.com>, stable-AT-vger.kernel.org, Hal Rosenstock <hal.rosenstock-AT-gmail.com>, Jason Gunthorpe <jgunthorpe-AT-obsidianresearch.com>, linux-mm-AT-kvack.org, Jeff Moyer <jmoyer-AT-redhat.com>, Ross Zwisler <ross.zwisler-AT-linux.intel.com>, Mauro Carvalho Chehab <mchehab-AT-kernel.org>, Christoph Hellwig <hch-AT-lst.de>, linux-media-AT-vger.kernel.org |
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 (3):
mm: introduce get_user_pages_longterm
IB/core: disable memory registration of fileystem-dax vmas
[media] v4l2: disable filesystem-dax mapping support
drivers/infiniband/core/umem.c | 2 -
drivers/media/v4l2-core/videobuf-dma-sg.c | 5 +-
include/linux/mm.h | 3 +
mm/gup.c | 75 +++++++++++++++++++++++++++++
4 files changed, 82 insertions(+), 3 deletions(-)
