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mm, devm_memremap_pages: use multi-order radix for ZONE_DEVICE lookups

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devm_memremap_pages() records mapped ranges in pgmap_radix with an entry
per section's worth of memory (128MB).  The key for each of those
entries is a section number.

This leads to false positives when devm_memremap_pages() is passed a
section-unaligned range as lookups in the misalignment fail to return
NULL.  We can close this hole by using the pfn as the key for entries in
the tree.  The number of entries required to describe a remapped range
is reduced by leveraging multi-order entries.

In practice this approach usually yields just one entry in the tree if
the size and starting address are of the same power-of-2 alignment.
Previously we always needed nr_entries = mapping_size / 128MB.

Link: https://lists.01.org/pipermail/linux-nvdimm/2016-August/006666.html
Link: http://lkml.kernel.org/r/150215410565.39310.13767886055248249438.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <[email protected]>
Reported-by: Toshi Kani <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Dan Williams 2017-09-06 16:24:13 -07:00 • committed by Linus Torvalds
commit ab1b597ee0
2 changed files with 39 additions and 14 deletions
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1
mm/Kconfig
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@ -678,6 +678,7 @@ config ZONE_DEVICE
depends on MEMORY_HOTREMOVE
depends on SPARSEMEM_VMEMMAP
depends on ARCH_HAS_ZONE_DEVICE
select RADIX_TREE_MULTIORDER
help
Device memory hotplug support allows for establishing pmem,