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 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 | 149 ++++- include/linux/mmzone.h | 2 + include/linux/page_ref.h | 10 + mm/gup.c | 598 +++++++++++++++----- mm/gup_benchmark.c | 74 ++- mm/huge_memory.c | 26 +- mm/hugetlb.c | 25 +- 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, 1109 insertions(+), 355 deletions(-) create mode 100644 Documentation/core-api/pin_user_pages.rst