mm, devm_memremap_pages: use multi-order radix for ZONE_DEVICE lookups
authorDan Williams <dan.j.williams@intel.com>
Wed, 6 Sep 2017 23:24:13 +0000 (16:24 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 7 Sep 2017 00:27:29 +0000 (17:27 -0700)
commitab1b597ee0e4208a1db227bb7b2c9512c8234b48
tree57d44937a91ae2e91e4c8bf741e6e4d326933064
parentc568da282bbc8f09c4b49201177fa259fe184c47
mm, devm_memremap_pages: use multi-order radix for ZONE_DEVICE lookups

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 <dan.j.williams@intel.com>
Reported-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/memremap.c
mm/Kconfig