[PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL_PIN

John Hubbard
2019-12-16T22:30:33Z

Hi,

This implements an API naming change (put_user_page*() -->
unpin_user_page*()), and also implements tracking of FOLL_PIN pages. It
extends that tracking to a few select subsystems. More subsystems will
be added in follow up work.

Christoph Hellwig, a point of interest:

a) I've moved the bulk of the code out of the inline functions, as
requested, for the devmap changes (patch 4: "mm: devmap: refactor
1-based refcounting for ZONE_DEVICE pages").

Changes since v10: Remaining fixes resulting from Jan Kara's reviews:

* Shifted to using the sign bit in page_dma_pinned() to allow accurate
results even in the overflow case. See the comments in that routine
for details. This allowed getting rid of the new
page_ref_zero_or_close_to_bias_overflow(), in favor of a simple
sign check via "page_ref_count() <= 0").

* Simplified some of the huge_memory.c changes, and simplified a gup.c
WARN invocation.

* Now using a standard -ENOMEM for most try_grab_page() failures.

* Got rid of tabs in the comment headers (I had thought they were
required there, but it's actually the reverse: they are not
allowed there).

* Rebased against 5.5-rc2 and retested.

* Added Jan Kara's reviewed-by tag for patch 23 (the main patch of the
series).

Changes since v9: Fixes resulting from Jan Kara's and Jonathan Corbet's
reviews:

* Removed reviewed-by tags from the "mm/gup: track FOLL_PIN pages" (those
were improperly inherited from the much smaller refactoring patch that
was merged into it).

* Made try_grab_compound_head() and try_grab_page() behavior similar in
their behavior with flags, in order to avoid "gotchas" later.

* follow_trans_huge_pmd(): moved the try_grab_page() to earlier in the
routine, in order to avoid having to undo mlock_vma_page().

* follow_hugetlb_page(): removed a refcount overflow check that is now
extraneous (and weaker than what try_grab_page() provides a few lines
further down).

* Fixed up two Documentation flaws, pointed out by Jonathan Corbet's
review.

Changes since v8:

* Merged the "mm/gup: pass flags arg to __gup_device_* functions" patch
into the "mm/gup: track FOLL_PIN pages" patch, as requested by
Christoph and Jan.

* Changed void grab_page() to bool try_grab_page(), and handled errors
at the call sites. (From Jan's review comments.) try_grab_page()
attempts to avoid page refcount overflows, even when counting up with
GUP_PIN_COUNTING_BIAS increments.

* Fixed a bug that I'd introduced, when changing a BUG() to a WARN().

* Added Jan's reviewed-by tag to the " mm/gup: allow FOLL_FORCE for
get_user_pages_fast()" patch.

* Documentation: pin_user_pages.rst: fixed an incorrect gup_benchmark
invocation, left over from the pin_longterm days, spotted while preparing
this version.

* Rebased onto today's linux.git (-rc1), and re-tested.

Changes since v7:

* Rebased onto Linux 5.5-rc1

* Reworked the grab_page() and try_grab_compound_head(), for API
consistency and less diffs (thanks to Jan Kara's reviews).

* Added Leon Romanovsky's reviewed-by tags for two of the IB-related
patches.

* patch 4 refactoring changes, as mentioned above.

There is a git repo and branch, for convenience:

git@github.com:johnhubbard/linux.git pin_user_pages_tracking_v8

For the remaining list of "changes since version N", those are all in
v7, which is here:

https://lore.kernel.org/r/20191121071354.456618-1-jhubbard@nvidia.com

============================================================
Overview:

This is a prerequisite to solving the problem of proper interactions
between file-backed pages, and [R]DMA activities, as discussed in [1],
[2], [3], and in a remarkable number of email threads since about
2017. :)

A new internal gup flag, FOLL_PIN is introduced, and thoroughly
documented in the last patch's Documentation/vm/pin_user_pages.rst.

I believe that this will provide a good starting point for doing the
layout lease work that Ira Weiny has been working on. That's because
these new wrapper functions provide a clean, constrained, systematically
named set of functionality that, again, is required in order to even
know if a page is "dma-pinned".

In contrast to earlier approaches, the page tracking can be
incrementally applied to the kernel call sites that, until now, have
been simply calling get_user_pages() ("gup"). In other words, opt-in by
changing from this:

get_user_pages() (sets FOLL_GET)
put_page()

to this:
pin_user_pages() (sets FOLL_PIN)
unpin_user_page()

============================================================
Testing:

* I've done some overall kernel testing (LTP, and a few other goodies),
and some directed testing to exercise some of the changes. And as you
can see, gup_benchmark is enhanced to exercise this. Basically, I've
been able to runtime test the core get_user_pages() and
pin_user_pages() and related routines, but not so much on several of
the call sites--but those are generally just a couple of lines
changed, each.

Not much of the kernel is actually using this, which on one hand
reduces risk quite a lot. But on the other hand, testing coverage
is low. So I'd love it if, in particular, the Infiniband and PowerPC
folks could do a smoke test of this series for me.

Runtime testing for the call sites so far is pretty light:

* io_uring: Some directed tests from liburing exercise this, and
they pass.
* process_vm_access.c: A small directed test passes.
* gup_benchmark: the enhanced version hits the new gup.c code, and
passes.
* infiniband: ran "ib_write_bw", which exercises the umem.c changes,
but not the other changes.
* VFIO: compiles (I'm vowing to set up a run time test soon, but it's
not ready just yet)
* powerpc: it compiles...
* drm/via: compiles...
* goldfish: compiles...
* net/xdp: compiles...
* media/v4l2: compiles...

[1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/
[2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/
[3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/

Dan Williams (1):
mm: Cleanup __put_devmap_managed_page() vs ->page_free()

John Hubbard (24):
mm/gup: factor out duplicate code from four routines
mm/gup: move try_get_compound_head() to top, fix minor issues
mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages
goldish_pipe: rename local pin_user_pages() routine
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM
vfio: fix FOLL_LONGTERM use, simplify get_user_pages_remote() call
mm/gup: allow FOLL_FORCE for get_user_pages_fast()
IB/umem: use get_user_pages_fast() to pin DMA pages
mm/gup: introduce pin_user_pages*() and FOLL_PIN
goldish_pipe: convert to pin_user_pages() and put_user_page()
IB/{core,hw,umem}: set FOLL_PIN via pin_user_pages*(), fix up ODP
mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote()
drm/via: set FOLL_PIN via pin_user_pages_fast()
fs/io_uring: set FOLL_PIN via pin_user_pages()
net/xdp: set FOLL_PIN via pin_user_pages()
media/v4l2-core: set pages dirty upon releasing DMA buffers
media/v4l2-core: pin_user_pages (FOLL_PIN) and put_user_page()
conversion
vfio, mm: pin_user_pages (FOLL_PIN) and put_user_page() conversion
powerpc: book3s64: convert to pin_user_pages() and put_user_page()
mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding
"1"
mm, tree-wide: rename put_user_page*() to unpin_user_page*()
mm/gup: track FOLL_PIN pages
mm/gup_benchmark: support pin_user_pages() and related calls
selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN
coverage

Documentation/core-api/index.rst | 1 +
Documentation/core-api/pin_user_pages.rst | 232 ++++++++
arch/powerpc/mm/book3s64/iommu_api.c | 10 +-
drivers/gpu/drm/via/via_dmablit.c | 6 +-
drivers/infiniband/core/umem.c | 19 +-
drivers/infiniband/core/umem_odp.c | 13 +-
drivers/infiniband/hw/hfi1/user_pages.c | 4 +-
drivers/infiniband/hw/mthca/mthca_memfree.c | 8 +-
drivers/infiniband/hw/qib/qib_user_pages.c | 4 +-
drivers/infiniband/hw/qib/qib_user_sdma.c | 8 +-
drivers/infiniband/hw/usnic/usnic_uiom.c | 4 +-
drivers/infiniband/sw/siw/siw_mem.c | 4 +-
drivers/media/v4l2-core/videobuf-dma-sg.c | 8 +-
drivers/nvdimm/pmem.c | 6 -
drivers/platform/goldfish/goldfish_pipe.c | 35 +-
drivers/vfio/vfio_iommu_type1.c | 35 +-
fs/io_uring.c | 6 +-
include/linux/mm.h | 155 ++++-
include/linux/mmzone.h | 2 +
include/linux/page_ref.h | 10 +
mm/gup.c | 626 +++++++++++++++-----
mm/gup_benchmark.c | 74 ++-
mm/huge_memory.c | 29 +-
mm/hugetlb.c | 38 +-
mm/memremap.c | 76 ++-
mm/process_vm_access.c | 28 +-
mm/swap.c | 24 +
mm/vmstat.c | 2 +
net/xdp/xdp_umem.c | 4 +-
tools/testing/selftests/vm/gup_benchmark.c | 21 +-
tools/testing/selftests/vm/run_vmtests | 22 +
31 files changed, 1145 insertions(+), 369 deletions(-)
create mode 100644 Documentation/core-api/pin_user_pages.rst

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2.24.1