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Commit b11a7b94 authored by Dan Williams's avatar Dan Williams Committed by Linus Torvalds
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mm: exclude ZONE_DEVICE from GFP_ZONE_TABLE 

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: 033fbae9 ("mm: ZONE_DEVICE for "device memory"")
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Reported-by: default avatarMark <markk@clara.co.uk>
Reported-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d334c9bc

include/linux/gfp.h

+20 −13
Original line number Diff line number Diff line
@@ -331,22 +331,29 @@ static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags) 
 *       0xe    => BAD (MOVABLE+DMA32+HIGHMEM)

 *       0xf    => BAD (MOVABLE+DMA32+HIGHMEM+DMA)

 *

 * ZONES_SHIFT must be <= 2 on 32 bit platforms.

 * GFP_ZONES_SHIFT must be <= 2 on 32 bit platforms.

 */



#if 16 * ZONES_SHIFT > BITS_PER_LONG

#error ZONES_SHIFT too large to create GFP_ZONE_TABLE integer

#if defined(CONFIG_ZONE_DEVICE) && (MAX_NR_ZONES-1) <= 4

/* ZONE_DEVICE is not a valid GFP zone specifier */

#define GFP_ZONES_SHIFT 2

#else

#define GFP_ZONES_SHIFT ZONES_SHIFT

#endif



#if 16 * GFP_ZONES_SHIFT > BITS_PER_LONG

#error GFP_ZONES_SHIFT too large to create GFP_ZONE_TABLE integer

#endif



#define GFP_ZONE_TABLE ( \

	(ZONE_NORMAL << 0 * ZONES_SHIFT)				      \

	| (OPT_ZONE_DMA << ___GFP_DMA * ZONES_SHIFT)			      \

	| (OPT_ZONE_HIGHMEM << ___GFP_HIGHMEM * ZONES_SHIFT)		      \

	| (OPT_ZONE_DMA32 << ___GFP_DMA32 * ZONES_SHIFT)		      \

	| (ZONE_NORMAL << ___GFP_MOVABLE * ZONES_SHIFT)			      \

	| (OPT_ZONE_DMA << (___GFP_MOVABLE | ___GFP_DMA) * ZONES_SHIFT)	      \

	| (ZONE_MOVABLE << (___GFP_MOVABLE | ___GFP_HIGHMEM) * ZONES_SHIFT)   \

	| (OPT_ZONE_DMA32 << (___GFP_MOVABLE | ___GFP_DMA32) * ZONES_SHIFT)   \

	(ZONE_NORMAL << 0 * GFP_ZONES_SHIFT)				       \

	| (OPT_ZONE_DMA << ___GFP_DMA * GFP_ZONES_SHIFT)		       \

	| (OPT_ZONE_HIGHMEM << ___GFP_HIGHMEM * GFP_ZONES_SHIFT)	       \

	| (OPT_ZONE_DMA32 << ___GFP_DMA32 * GFP_ZONES_SHIFT)		       \

	| (ZONE_NORMAL << ___GFP_MOVABLE * GFP_ZONES_SHIFT)		       \

	| (OPT_ZONE_DMA << (___GFP_MOVABLE | ___GFP_DMA) * GFP_ZONES_SHIFT)    \

	| (ZONE_MOVABLE << (___GFP_MOVABLE | ___GFP_HIGHMEM) * GFP_ZONES_SHIFT)\

	| (OPT_ZONE_DMA32 << (___GFP_MOVABLE | ___GFP_DMA32) * GFP_ZONES_SHIFT)\

)



/*
@@ -371,8 +378,8 @@ static inline enum zone_type gfp_zone(gfp_t flags) 
	enum zone_type z;

	int bit = (__force int) (flags & GFP_ZONEMASK);



	z = (GFP_ZONE_TABLE >> (bit * ZONES_SHIFT)) &

					 ((1 << ZONES_SHIFT) - 1);

	z = (GFP_ZONE_TABLE >> (bit * GFP_ZONES_SHIFT)) &

					 ((1 << GFP_ZONES_SHIFT) - 1);

	VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);

	return z;

}

include/linux/page-flags-layout.h

+2 −0
Original line number Diff line number Diff line
@@ -17,6 +17,8 @@ 
#define ZONES_SHIFT 1

#elif MAX_NR_ZONES <= 4

#define ZONES_SHIFT 2

#elif MAX_NR_ZONES <= 8

#define ZONES_SHIFT 3

#else

#error ZONES_SHIFT -- too many zones configured adjust calculation

#endif

mm/Kconfig

+0 −2
Original line number Diff line number Diff line
@@ -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