[PATCH v4 0/3] iommu/io-pgtable-arm-v7s: Use DMA32 zone for page tables

Nicolas Boichat
2018-12-05T05:48:48Z

This is a follow-up to the discussion in [1], [2].

IOMMUs using ARMv7 short-descriptor format require page tables
(level 1 and 2) to be allocated within the first 4GB of RAM, even
on 64-bit systems.

For L1 tables that are bigger than a page, we can just use __get_free_pages
with GFP_DMA32 (on arm64 systems only, arm would still use GFP_DMA).

For L2 tables that only take 1KB, it would be a waste to allocate a full
page, so we considered 3 approaches:
1. This series, adding support for GFP_DMA32 slab caches.
2. genalloc, which requires pre-allocating the maximum number of L2 page
tables (4096, so 4MB of memory).
3. page_frag, which is not very memory-efficient as it is unable to reuse
freed fragments until the whole page is freed. [3]

This series is the most memory-efficient approach.

[1] https://lists.linuxfoundation.org/pipermail/iommu/2018-November/030876.html
[2] https://lists.linuxfoundation.org/pipermail/iommu/2018-December/031696.html
[3] https://patchwork.codeaurora.org/patch/671639/

Changes since v1:
- Add support for SLAB_CACHE_DMA32 in slab and slub (patches 1/2)
- iommu/io-pgtable-arm-v7s (patch 3):
- Changed approach to use SLAB_CACHE_DMA32 added by the previous
commit.
- Use DMA or DMA32 depending on the architecture (DMA for arm,
DMA32 for arm64).

Changes since v2:
- Reworded and expanded commit messages
- Added cache_dma32 documentation in PATCH 2/3.

v3 used the page_frag approach, see [3].

Nicolas Boichat (3):
mm: slab/slub: Add check_slab_flags function to check for valid flags
mm: Add support for kmem caches in DMA32 zone
iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging

Documentation/ABI/testing/sysfs-kernel-slab | 9 ++++++++
drivers/iommu/io-pgtable-arm-v7s.c | 20 +++++++++++++----
include/linux/slab.h | 2 ++
mm/internal.h | 22 +++++++++++++++++--
mm/slab.c | 10 +++------
mm/slab.h | 3 ++-
mm/slab_common.c | 2 +-
mm/slub.c | 24 +++++++++++++++------
8 files changed, 70 insertions(+), 22 deletions(-)

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2.20.0.rc1.387.gf8505762e3-goog