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Date:   Fri,  7 Dec 2018 14:16:17 +0800
From:   Nicolas Boichat <>
To:     Will Deacon <>
Cc:     Robin Murphy <>,
        Joerg Roedel <>,
        Christoph Lameter <>,
        Pekka Enberg <>,
        David Rientjes <>,
        Joonsoo Kim <>,
        Andrew Morton <>,
        Vlastimil Babka <>,
        Michal Hocko <>,
        Mel Gorman <>,
        Levin Alexander <>,
        Huaisheng Ye <>,
        Mike Rapoport <>,,,,, Yong Wu <>,
        Matthias Brugger <>,
        Tomasz Figa <>,,, Matthew Wilcox <>
Subject: [PATCH v5 0/3] iommu/io-pgtable-arm-v7s: Use DMA32 zone for page tables

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.


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
   - 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].

Changes since v4:
 - Dropped change that removed GFP_DMA32 from GFP_SLAB_BUG_MASK:
   instead we can just call kmem_cache_*alloc without GFP_DMA32
   parameter. This also means that we can drop PATCH v4 1/3, as we
   do not make any changes in GFP flag verification.
 - Dropped hunks that added cache_dma32 sysfs file, and moved
   the hunks to PATCH v5 3/3, so that maintainer can decide whether
   to pick the change independently.

Nicolas Boichat (3):
  mm: Add support for kmem caches in DMA32 zone
  iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging
  mm: Add /sys/kernel/slab/cache/cache_dma32

 Documentation/ABI/testing/sysfs-kernel-slab |  9 +++++++++
 drivers/iommu/io-pgtable-arm-v7s.c          | 19 +++++++++++++++----
 include/linux/slab.h                        |  2 ++
 mm/slab.c                                   |  2 ++
 mm/slab.h                                   |  3 ++-
 mm/slab_common.c                            |  2 +-
 mm/slub.c                                   | 16 ++++++++++++++++
 tools/vm/slabinfo.c                         |  7 ++++++-
 8 files changed, 53 insertions(+), 7 deletions(-)


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