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mm: exclude ZONE_DEVICE from GFP_ZONE_TABLE

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ZONE_DEVICE (merged in 4.3) and ZONE_CMA (proposed) are examples of new
mm zones that are bumping up against the current maximum limit of 4
zones, i.e.  2 bits in page->flags for the GFP_ZONE_TABLE.

The GFP_ZONE_TABLE poses an interesting constraint since
include/linux/gfp.h gets included by the 32-bit portion of a 64-bit
build.  We need to be careful to only build the table for zones that
have a corresponding gfp_t flag.  GFP_ZONES_SHIFT is introduced for this
purpose.  This patch does not attempt to solve the problem of adding a
new zone that also has a corresponding GFP_ flag.

Vlastimil points out that ZONE_DEVICE, by depending on x86_64 and
SPARSEMEM_VMEMMAP implies that SECTIONS_WIDTH is zero.  In other words
even though ZONE_DEVICE does not fit in GFP_ZONE_TABLE it is free to
consume another bit in page->flags (expand ZONES_WIDTH) with room to
spare.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=110931
Fixes: 033fbae988 ("mm: ZONE_DEVICE for "device memory"")
Signed-off-by: Dan Williams <[email protected]>
Reported-by: Mark <[email protected]>
Reported-by: Vlastimil Babka <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Sudip Mukherjee <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Dan Williams 2016-03-17 14:19:41 -07:00 • committed by Linus Torvalds
commit b11a7b9410
3 changed files with 22 additions and 15 deletions
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mm/Kconfig
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@ -651,8 +651,6 @@ config IDLE_PAGE_TRACKING
config ZONE_DEVICE
bool "Device memory (pmem, etc...) hotplug support" if EXPERT
default !ZONE_DMA
depends on !ZONE_DMA
depends on MEMORY_HOTPLUG
depends on MEMORY_HOTREMOVE
depends on X86_64 #arch_add_memory() comprehends device memory