Hi Christoph, David, Lorenzo,
Here are three patches that go on top of the similar patches for bio
structs now in the block tree that make the old block direct-IO code use
iov_iter_extract_pages() and page pinning.
There are three patches:
(1) Make page pinning neither add nor remove a pin to/from a ZERO_PAGE,
thereby allowing the dio code to insert zero pages in the middle of
dealing with pinned pages. This also mitigates a potential problem
whereby userspace could force the overrun the pin counter of a zero
page.
A pair of functions are provided to wrap the testing of a page or
folio to see if it is a zero page.
(2) Provide a function to allow an additional pin to be taken on a page we
already have pinned (and do nothing for a zero page).
(3) Switch direct-io.c over to using page pinning and to use
iov_iter_extract_pages() so that pages from non-user-backed iterators
aren't pinned.
I've pushed the patches here also:
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-old-dio
David
Changes
=======
ver #3)
- Move is_zero_page() and is_zero_folio() to mm.h for dependency reasons.
- Add more comments and adjust the docs about pinning zero pages.
- Rename page_get_additional_pin() to folio_add_pin().
- Use is_zero_folio() in folio_add_pin().
- Rename need_unpin to is_pinned in struct dio.
ver #2)
- Fix use of ZERO_PAGE().
- Add wrappers for testing if a page is a zero page.
- Return the zero page obtained, not ZERO_PAGE(0) unconditionally.
- Need to set BIO_PAGE_PINNED conditionally, and not BIO_PAGE_REFFED.
Link: https://lore.kernel.org/r/ZGxfrOLZ4aN9/MvE@xxxxxxxxxxxxx/ [1]
Link: https://lore.kernel.org/r/20230525155102.87353-1-dhowells@xxxxxxxxxx/ # v1
Link: https://lore.kernel.org/r/20230525223953.225496-1-dhowells@xxxxxxxxxx/ # v2
David Howells (3):
mm: Don't pin ZERO_PAGE in pin_user_pages()
mm: Provide a function to get an additional pin on a page
block: Use iov_iter_extract_pages() and page pinning in direct-io.c
Documentation/core-api/pin_user_pages.rst | 6 ++
fs/direct-io.c | 72 ++++++++++++++---------
include/linux/mm.h | 27 ++++++++-
mm/gup.c | 58 +++++++++++++++++-
4 files changed, 131 insertions(+), 32 deletions(-)
