From b3d40a2b6d10c9d0424d2b398bf962fb6adad87e Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Tue, 22 Mar 2022 14:43:20 -0700 Subject: mm: enforce pageblock_order < MAX_ORDER Some places in the kernel don't really expect pageblock_order >= MAX_ORDER, and it looks like this is only possible in corner cases: 1) CONFIG_DEFERRED_STRUCT_PAGE_INIT we'll end up freeing pageblock_order pages via __free_pages_core(), which cannot possibly work. 2) find_zone_movable_pfns_for_nodes() will roundup the ZONE_MOVABLE start PFN to MAX_ORDER_NR_PAGES. Consequently with a bigger pageblock_order, we could have a single pageblock partially managed by two zones. 3) compaction code runs into __fragmentation_index() with order >= MAX_ORDER, when checking WARN_ON_ONCE(order >= MAX_ORDER). [1] 4) mm/page_reporting.c won't be reporting any pages with default page_reporting_order == pageblock_order, as we'll be skipping the reporting loop inside page_reporting_process_zone(). 5) __rmqueue_fallback() will never be able to steal with ALLOC_NOFRAGMENT. pageblock_order >= MAX_ORDER is weird either way: it's a pure optimization for making alloc_contig_range(), as used for allcoation of gigantic pages, a little more reliable to succeed. However, if there is demand for somewhat reliable allocation of gigantic pages, affected setups should be using CMA or boottime allocations instead. So let's make sure that pageblock_order < MAX_ORDER and simplify. [1] https://lkml.kernel.org/r/87r189a2ks.fsf@linux.ibm.com Link: https://lkml.kernel.org/r/20220214174132.219303-3-david@redhat.com Signed-off-by: David Hildenbrand Reviewed-by: Zi Yan Cc: Aneesh Kumar K.V Cc: Benjamin Herrenschmidt Cc: Christoph Hellwig Cc: Frank Rowand Cc: John Garry via iommu Cc: Marek Szyprowski Cc: Michael Ellerman Cc: Michael S. Tsirkin Cc: Minchan Kim Cc: Paul Mackerras Cc: Rob Herring Cc: Robin Murphy Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/Kconfig | 3 +++ 1 file changed, 3 insertions(+) (limited to 'mm/Kconfig') diff --git a/mm/Kconfig b/mm/Kconfig index 3326ee3903f3..4c91b92e7537 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -262,6 +262,9 @@ config HUGETLB_PAGE_SIZE_VARIABLE HUGETLB_PAGE_ORDER when there are multiple HugeTLB page sizes available on a platform. + Note that the pageblock_order cannot exceed MAX_ORDER - 1 and will be + clamped down to MAX_ORDER - 1. + config CONTIG_ALLOC def_bool (MEMORY_ISOLATION && COMPACTION) || CMA -- cgit v1.2.3