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@xxxxxxxxxxxxx [2] https://lkml.kernel.org/r/20220211164135.1803616-1-zi.yan@xxxxxxxx Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Aneesh Kumar K V <aneesh.kumar@xxxxxxxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: Paul Mackerras <paulus@xxxxxxxxx> Cc: Rob Herring <robh+dt@xxxxxxxxxx> Cc: Frank Rowand <frowand.list@xxxxxxxxx> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Cc: Robin Murphy <robin.murphy@xxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx Cc: devicetree@xxxxxxxxxxxxxxx Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx Cc: linux-mm@xxxxxxxxx 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
