From: John Hubbard <jhubbard@xxxxxxxxxx>
Here is an updated proposal for tracking pages that have had
get_user_pages*() called on them. This is in support of fixing the problem
discussed in [1]. This RFC only shows how to set up a reliable
PageDmaPinned flag. What to *do* with that flag is left for a later
discussion.
I'm providing this in order to help the discussion about patches 1-3, which
I'm hoping to check in first. The sequence would be:
-- apply patches 1-3, convert the rest of the subsystems to call
put_user_page*(), then
-- apply patches 4-6, then
-- Apply more patches, to actually use the new PageDmaPinned flag.
One question up front is, "how do we ensure that either put_user_page()
or put_page() are called, depending on whether the page came from
get_user_pages() or not?". From this series, you can see that:
-- It's possible to assert within put_user_page(), that we are in the
right place.
-- It's less clear that there is a way to assert within put_page(),
because put_page() is called from put_user_page(), and PageDmaPinned
may or may not be set--either case is valid.
Opinions and ideas are welcome there.
This is a lightly tested example (it boots up on x86_64, and just lets the
dma-pinned pages leak, in all non-infiniband cases...which is all cases, on
my particular test computer). This series just does the following:
a) Provides the put_user_page*() routines that have been discussed in
another thread (patch 2).
b) Provides a single example of converting some code (infiniband) to use
those routines (patch 3).
c) Connects up get_user_pages*() to use the new refcounting and flags
fieldsj (patches 4-6)
[1] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()"
John Hubbard (6):
mm: get_user_pages: consolidate error handling
mm: introduce put_user_page*(), placeholder versions
infiniband/mm: convert put_page() to put_user_page*()
mm: introduce page->dma_pinned_flags, _count
mm: introduce zone_gup_lock, for dma-pinned pages
mm: track gup pages with page->dma_pinned_* fields
drivers/infiniband/core/umem.c | 7 +-
drivers/infiniband/core/umem_odp.c | 2 +-
drivers/infiniband/hw/hfi1/user_pages.c | 11 +-
drivers/infiniband/hw/mthca/mthca_memfree.c | 6 +-
drivers/infiniband/hw/qib/qib_user_pages.c | 11 +-
drivers/infiniband/hw/qib/qib_user_sdma.c | 6 +-
drivers/infiniband/hw/usnic/usnic_uiom.c | 7 +-
include/linux/mm.h | 9 ++
include/linux/mm_types.h | 22 +++-
include/linux/mmzone.h | 6 +
include/linux/page-flags.h | 47 +++++++
mm/gup.c | 93 +++++++++++---
mm/memcontrol.c | 7 +
mm/page_alloc.c | 1 +
mm/swap.c | 134 ++++++++++++++++++++
15 files changed, 319 insertions(+), 50 deletions(-)
--
2.19.1
