[PATCH 00/19] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM
jhubbard at nvidia.com
Wed Oct 30 22:49:11 UTC 2019
This applies cleanly to linux-next and mmotm, and also to linux.git if
linux-next's commit 20cac10710c9 ("mm/gup_benchmark: fix MAP_HUGETLB
case") is first applied there.
This provides tracking of dma-pinned pages. This is a prerequisite to
solving the larger problem of proper interactions between file-backed
pages, and [R]DMA activities, as discussed in , , , 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)
pin_user_pages() (sets FOLL_PIN)
Because there are interdependencies with FOLL_LONGTERM, a similar
conversion as for FOLL_PIN, was applied. The change was from this:
get_user_pages(FOLL_LONGTERM) (also sets FOLL_GET)
pin_longterm_pages() (sets FOLL_PIN | FOLL_LONGTERM)
* Patches 1-4: refactoring and preparatory cleanup, independent fixes
(Patch 4: V4L2-core bug fix (can be separately applied))
* Patch 5: introduce pin_user_pages(), FOLL_PIN, but no functional
* Patches 6-11: Convert existing put_user_page() callers, to use the
* Patch 12: Activate tracking of FOLL_PIN pages.
* Patches 13-15: convert FOLL_LONGTERM callers
* Patches: 16-17: gup_benchmark and run_vmtests support
* Patch 18: enforce FOLL_LONGTERM as a gup-internal (only) flag
* Patch 19: Documentation/vm/pin_user_pages.rst
* 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.
Also, my runtime testing for the call sites so far is very weak:
* 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 (still only have crude "IB pingpong" working, on a
good day: it's not exercising my conversions at runtime...)
* 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...
* Get the block/bio_vec sites converted to use pin_user_pages().
* Work with Ira and Dave Chinner to weave this together with the
layout lease stuff.
 Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/
 DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/
 The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/
John Hubbard (19):
mm/gup: pass flags arg to __gup_device_* functions
mm/gup: factor out duplicate code from four routines
goldish_pipe: rename local pin_user_pages() routine
media/v4l2-core: set pages dirty upon releasing DMA buffers
mm/gup: introduce pin_user_pages*() and FOLL_PIN
goldish_pipe: convert to pin_user_pages() and put_user_page()
infiniband: set FOLL_PIN, FOLL_LONGTERM via pin_longterm_pages*()
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()
mm/gup: track FOLL_PIN pages
media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user_page()
vfio, mm: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion
powerpc: book3s64: convert to pin_longterm_pages() and put_user_page()
mm/gup_benchmark: support pin_user_pages() and related calls
selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN
mm/gup: remove support for gup(FOLL_LONGTERM)
Documentation/vm: add pin_user_pages.rst
Documentation/vm/index.rst | 1 +
Documentation/vm/pin_user_pages.rst | 213 +++++++
arch/powerpc/mm/book3s64/iommu_api.c | 15 +-
drivers/gpu/drm/via/via_dmablit.c | 2 +-
drivers/infiniband/core/umem.c | 5 +-
drivers/infiniband/core/umem_odp.c | 10 +-
drivers/infiniband/hw/hfi1/user_pages.c | 4 +-
drivers/infiniband/hw/mthca/mthca_memfree.c | 3 +-
drivers/infiniband/hw/qib/qib_user_pages.c | 8 +-
drivers/infiniband/hw/qib/qib_user_sdma.c | 2 +-
drivers/infiniband/hw/usnic/usnic_uiom.c | 9 +-
drivers/infiniband/sw/siw/siw_mem.c | 5 +-
drivers/media/v4l2-core/videobuf-dma-sg.c | 10 +-
drivers/platform/goldfish/goldfish_pipe.c | 35 +-
drivers/vfio/vfio_iommu_type1.c | 15 +-
fs/io_uring.c | 5 +-
include/linux/mm.h | 133 ++++-
include/linux/mmzone.h | 2 +
include/linux/page_ref.h | 10 +
mm/gup.c | 622 ++++++++++++++++----
mm/gup_benchmark.c | 81 ++-
mm/huge_memory.c | 32 +-
mm/hugetlb.c | 28 +-
mm/memremap.c | 4 +-
mm/process_vm_access.c | 28 +-
mm/vmstat.c | 2 +
net/xdp/xdp_umem.c | 4 +-
tools/testing/selftests/vm/gup_benchmark.c | 28 +-
tools/testing/selftests/vm/run_vmtests | 22 +
29 files changed, 1066 insertions(+), 272 deletions(-)
create mode 100644 Documentation/vm/pin_user_pages.rst
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