Commit 3f135355 authored Jan 30, 2020 by Kirill A. Shutemov Committed by Linus Torvalds Jan 31, 2020

mm/page_alloc: skip non present sections on zone initialization

memmap_init_zone() can be called on the ranges with holes during the
boot.  It will skip any non-valid PFNs one-by-one.  It works fine as
long as holes are not too big.

But huge holes in the memory map causes a problem.  It takes over 20
seconds to walk 32TiB hole.  x86-64 with 5-level paging allows for much
larger holes in the memory map which would practically hang the system.

Deferred struct page init doesn't help here.  It only works on the
present ranges.

Skipping non-present sections would fix the issue.

Link: http://lkml.kernel.org/r/20191230093828.24613-1-kirill.shutemov@linux.intel.com


Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Jin, Zhi" <zhi.jin@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 7b69d79f

mm/page_alloc.c

+27 −1

Original line number	Diff line number	Diff line
		@@ -5848,6 +5848,30 @@ overlap_memmap_init(unsigned long zone, unsigned long *pfn)
		return false;
		}

		#ifdef CONFIG_SPARSEMEM
		/* Skip PFNs that belong to non-present sections */
		static inline __meminit unsigned long next_pfn(unsigned long pfn)
		{
		unsigned long section_nr;

		section_nr = pfn_to_section_nr(++pfn);
		if (present_section_nr(section_nr))
		return pfn;

		while (++section_nr <= __highest_present_section_nr) {
		if (present_section_nr(section_nr))
		return section_nr_to_pfn(section_nr);
		}

		return -1;
		}
		#else
		static inline __meminit unsigned long next_pfn(unsigned long pfn)
		{
		return pfn++;
		}
		#endif

		/*
		* Initially all pages are reserved - free ones are freed
		* up by memblock_free_all() once the early boot process is
		@@ -5887,8 +5911,10 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
		* function. They do not exist on hotplugged memory.
		*/
		if (context == MEMMAP_EARLY) {
		if (!early_pfn_valid(pfn))
		if (!early_pfn_valid(pfn)) {
		pfn = next_pfn(pfn) - 1;
		continue;
		}
		if (!early_pfn_in_nid(pfn, nid))
		continue;
		if (overlap_memmap_init(zone, &pfn))

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