[PATCH v6 0/5] nfs: modernize direct I/O path
Pranjal Shrivastava <[email protected]>
| Newsgroups | org.kernel.vger.linux-nfs,org.kernel.vger.linux-kernel,org.kernel.vger.linux-pci,org.kernel.vger.linux-rdma |
|---|---|
| Message-ID | <[email protected]> |
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 different series. Additionally, based on the discussion in the v2 [2] of this series, the migration of NFS Direct I/O to folios would be handled in a separate follow-up 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. 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. Upcoming Work / Roadmap ================================ As decided in the RFC [1] & v2 [2], there will be separate series for P2PDMA Enablement and Migrating NFS Direct I/O to use folios. This series lays the necessary groundwork for the upcoming work. Following this, two additional series are planned: 1. Migrating NFS Direct I/O to Folios A series that introduces and exports helper from iov_iter.c to allow the nfs_direct_extract_pages() helper introduced here to aggregate multiple pages into a single large folio-based request, aiming to reduce the RPC overhead for hugepage I/O. 2. P2PDMA Enablement for NFS Enabling ITER_ALLOW_P2PDMA for the Direct I/O path and introducing transport-level negotiation (discovery of P2P-capable RDMA/NVMe devices). This will build upon the PG_PINNED infrastructure introduced by this series. Testing ======= This series has been tested with xfstests [3] on RDMA & TCP transports by running the quick test suite for each transport vs. version combo: ./check -g quick -s rdma3 -s rdma40 -s rdma41 -s rdma42 -s tcp3 -s tcp40 -s tcp41 -s tcp42 The tests were run before & after applying the series. No regressions were observed. The following summary was tabulated via a custom script [4] (on github) to depict that the tests failing in v1 [5] are now passing. 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/[email protected]/ [2] https://lore.kernel.org/all/[email protected]/ [3] https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git [4] https://github.com/pran005/tools/blob/main/display.py [5] https://lore.kernel.org/all/[email protected]/ [v6] - Fixed double unpin bugs pointed out by Sashiko: https://sashiko.dev/#/patchset/20260810195040.2877784-1-praan%40google.com - Added R-bs from Christoph (due since v4) [v5] - https://lore.kernel.org/all/[email protected]/ - Fixed an iov_iter_revert oops in nfs_direct_extract_pages(). - Fixed a refcount underflow in nfs_direct_release_pages() during swap-over-NFS by ensuring we do not call put_page() on unpinned memory. - Rebased on fs-next [v4] - https://lore.kernel.org/all/[email protected]/ - Dropped superfluous externs in include/linux/nfs_page.h - Scoped `req` locally inside the loop in nfs_release_request_list() - Wrapped >80 character lines in Patch 1 to adhere to coding style. - Fixed typos and capitalization convention in the commit msgs - Collected Reviewed-by tags from Christoph and Shivaji - Rebased on fs-next [v3] - https://lore.kernel.org/all/[email protected]/ - Dropped patches that added folio support for NFS Direct I/O - Folded requested_bytes accounting in patch 5 due to dropped folio support - Rebased on fs-next [v2] - https://lore.kernel.org/all/[email protected]/ - 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/[email protected]/ Pranjal Shrivastava (5): 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 fs/nfs/direct.c | 139 ++++++++++++++++++++------------------- fs/nfs/pagelist.c | 66 ++++++++++++++++--- fs/nfs/read.c | 2 +- fs/nfs/write.c | 2 +- include/linux/nfs_page.h | 8 ++- 5 files changed, 134 insertions(+), 83 deletions(-) base-commit: 15db403711f3cd9b7b764716ddf5909091b604bf -- 2.55.0.691.gc56d675ccc-goog