[RFC PATCH v2 0/3] block: Make old dio use iov_iter_extract_pages() and page pinning

From: David Howells
Date: Thu May 25 2023 - 18:41:08 EST

Hi Christoph, David,

Since Christoph asked nicely[1] ;-), 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 not add or 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.

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:



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

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

fs/direct-io.c | 72 ++++++++++++++++++++++++-----------------
include/linux/mm.h | 1 +
include/linux/pgtable.h | 10 ++++++
mm/gup.c | 54 ++++++++++++++++++++++++++++++-
4 files changed, 107 insertions(+), 30 deletions(-)