[PATCH v2 0/7] nfs: Modernize Direct I/O path

[Pranjal Shrivastava <praan@google.com>]

Modernize the NFS Direct I/O path as a preparatory step to enable PCI
Peer-to-Peer DMA (P2PDMA) support. Following feedback on the initial
RFC [1], the modernization and architectural changes are split into
this standalone series.

Currently, NFS O_DIRECT relies on the legacy iov_iter_get_pages_alloc2()
API which does not support the pinning requirements for P2P memory.
The implementation moves NFS to the modern iov_iter_extract_pages() API
and migrates NFS direct I/O away from pages to use folios.

Design
======

1. Pin-Awareness
Standard NFS requests use get_page() and put_page() for memory
management. However, memory extracted via iov_iter_extract_pages()
requires explicit pinning.

Introduce a PG_PINNED flag and a wb_nr_pinned count to struct nfs_page.
This allows the request lifecycle to track ownership of physical pins
and ensure that unpinning is performed only when the I/O is complete.

2. API Migration
Migrate the Direct I/O path to the modern iov_iter_extract_pages()
API. This aligns NFS with the modern extraction model and serves as
the foundation for passing ITER_ALLOW_P2PDMA in a follow-up series.

3. Extraction Helper and Folio Support
Introduce a new extraction helper in direct.c to group contiguous
pages from the same folio into a single struct nfs_page. This
effectively migrates the Direct I/O path from being page-based to being
folio-based.

Note: zone_device_pages_have_same_pgmap() checks are intentionally
omitted in the extraction helper since P2PDMA enablement will be
introduced in a follow-up series.

Bisectability
=============
The series attempts to remain bisectable. 

[Patches 1-2] Introduce pin-aware infrastructure and accounting.
[Patch 3] Adds a centralized request release helper.
[Patch 4] Migrates the Direct I/O path to iov_iter_extract_pages().
[Patches 5-6] Implement the extraction helper and folio-based grouping.
[Patch 7] Removes orphaned page-based helpers.

Testing
=======
This series has been tested with xfstests [2] on RDMA & TCP transports:

 ./check generic/091 generic/130 generic/139 generic/143 generic/154 \
         generic/155 generic/183 generic/188 generic/190 generic/196 \
         generic/198 generic/203 generic/214 generic/240 generic/263 \
         generic/287 generic/290 generic/292 generic/330 generic/444 \
         generic/450 generic/451 generic/586 generic/647 generic/708 \
         generic/729 generic/760

The following summary was tabulated via a custom script [3] (on github).

python3 display.py results/*/check.log
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| testcase     | rdma-sys-3   | rdma-sys-4.0 | rdma-sys-4.1 | rdma-sys-4.2 | tcp-sys-3    | tcp-sys-4.0  | tcp-sys-4.1  | tcp-sys-4.2  |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| generic/091  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/130  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/139  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/143  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/154  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/155  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/183  | skipped      | skipped      | skipped      | pass         | skipped      | skipped      | skipped      | pass         |
| generic/188  | skipped      | skipped      | skipped      | pass         | skipped      | skipped      | skipped      | pass         |
| generic/190  | skipped      | skipped      | skipped      | pass         | skipped      | skipped      | skipped      | pass         |
| generic/196  | skipped      | skipped      | skipped      | pass         | skipped      | skipped      | skipped      | pass         |
| generic/198  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/203  | skipped      | skipped      | skipped      | pass         | skipped      | skipped      | skipped      | pass         |
| generic/214  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/240  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/263  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/287  | skipped      | skipped      | skipped      | pass         | skipped      | skipped      | skipped      | pass         |
| generic/290  | skipped      | skipped      | skipped      | pass         | skipped      | skipped      | skipped      | pass         |
| generic/292  | skipped      | skipped      | skipped      | pass         | skipped      | skipped      | skipped      | pass         |
| generic/330  | skipped      | skipped      | skipped      | pass         | skipped      | skipped      | skipped      | pass         |
| generic/444  | skipped      | skipped      | skipped      | skipped      | skipped      | skipped      | skipped      | skipped      |
| generic/450  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/451  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/586  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/647  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/708  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/729  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
| generic/760  | pass         | pass         | pass         | pass         | pass         | pass         | pass         | pass         |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+

Thanks,
Praan

[1] https://lore.kernel.org/all/20260401194501.2269200-1-praan@google.com/
[2] https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git


[v2] 
 - Fix data corruption in nfs_direct_extract_pages() by correctly
   calculating intra-page offsets using offset_in_page().
 - Fix requested_bytes accounting in direct read/write paths to only
   increment after successful RPC scheduling.
 - Add missing kernel-doc descriptions for the @pinned parameter in
   nfs_page_create_from_page() and nfs_page_create_from_folio().
 - Rebase on fs-next/

[v1] https://lore.kernel.org/all/20260603053033.3300318-1-praan@google.com/

Pranjal Shrivastava (7):
  nfs: make nfs_page pin-aware
  nfs: Track number of pinned pages in nfs_page
  nfs: Introduce nfs_release_request_list helper
  nfs: migrate direct I/O to iov_iter_extract_pages
  nfs: introduce nfs_direct_extract_pages helper
  nfs: Optimize direct I/O to use folios for requests
  nfs: Cleanup the nfs_page_create_from_page helper

 fs/nfs/direct.c          | 165 +++++++++++++++++++++++----------------
 fs/nfs/pagelist.c        |  87 +++++++++++----------
 fs/nfs/read.c            |   2 +-
 fs/nfs/write.c           |   2 +-
 include/linux/nfs_page.h |  12 ++-
 5 files changed, 150 insertions(+), 118 deletions(-)


base-commit: 389bb4a76905771adfa86d21ee0b865247148e9d
-- 
2.54.0.1136.gdb2ca164c4-goog