[PATCH v1 0/2] mm: enforce pageblock_order < MAX_ORDER

[David Hildenbrand]

Having pageblock_order >= MAX_ORDER seems to be able to happen in corner
cases and some parts of the kernel are not prepared for it.

For example, Aneesh has shown [1] that such kernels can be compiled on
ppc64 with 64k base pages by setting FORCE_MAX_ZONEORDER=8, which will run
into a WARN_ON_ONCE(order >= MAX_ORDER) in comapction code right during
boot.

We can get pageblock_order >= MAX_ORDER when the default hugetlb size is
bigger than the maximum allocation granularity of the buddy, in which case
we are no longer talking about huge pages but instead gigantic pages.

Having pageblock_order >= MAX_ORDER can only make alloc_contig_range() of
such gigantic pages more likely to succeed.

Reliable use of gigantic pages either requires boot time allcoation or CMA,
no need to overcomplicate some places in the kernel to optimize for corner
cases that are broken in other areas of the kernel.

Let's enforce pageblock_order < MAX_ORDER and simplify.

Especially patch #1 can be regarded a cleanup before:
	[PATCH v5 0/6] Use pageblock_order for cma and alloc_contig_range
	alignment. [2]

[1] https://lkml.kernel.org/r/87r189a2ks.fsf@linux.ibm.com
[2] https://lkml.kernel.org/r/20220211164135.1803616-1-zi.yan@sent.com

Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Aneesh Kumar K V <aneesh.kumar at linux.ibm.com>
Cc: Zi Yan <ziy at nvidia.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Rob Herring <robh+dt at kernel.org>
Cc: Frank Rowand <frowand.list at gmail.com>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: Christoph Hellwig <hch at lst.de>
Cc: Marek Szyprowski <m.szyprowski at samsung.com>
Cc: Robin Murphy <robin.murphy at arm.com>
Cc: Minchan Kim <minchan at kernel.org>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: linuxppc-dev at lists.ozlabs.org
Cc: devicetree at vger.kernel.org
Cc: virtualization at lists.linux-foundation.org
Cc: iommu at lists.linux-foundation.org
Cc: linux-mm at kvack.org

David Hildenbrand (2):
  cma: factor out minimum alignment requirement
  mm: enforce pageblock_order < MAX_ORDER

 arch/powerpc/include/asm/fadump-internal.h |  5 ----
 arch/powerpc/kernel/fadump.c               |  2 +-
 drivers/of/of_reserved_mem.c               |  9 ++----
 drivers/virtio/virtio_mem.c                |  9 ++----
 include/linux/cma.h                        |  8 ++++++
 include/linux/pageblock-flags.h            |  7 +++--
 kernel/dma/contiguous.c                    |  4 +--
 mm/Kconfig                                 |  3 ++
 mm/cma.c                                   | 20 ++++----------
 mm/page_alloc.c                            | 32 ++++++----------------
 10 files changed, 37 insertions(+), 62 deletions(-)


base-commit: 754e0b0e35608ed5206d6a67a791563c631cec07
-- 
2.34.1