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Subject[RFC PATCH v3 1/9] include/linux/gfp.h: get rid of GFP_ZONE_TABLE/BAD
Date
From: Huaisheng Ye <yehs1@lenovo.com>

Replace GFP_ZONE_TABLE and GFP_ZONE_BAD with encoded zone number.

Delete ___GFP_DMA, ___GFP_HIGHMEM and ___GFP_DMA32 from GFP bitmasks,
the bottom three bits of GFP mask is reserved for storing encoded
zone number.

The encoding method is XOR. Get zone number from enum zone_type,
then encode the number with ZONE_NORMAL by XOR operation.
The goal is to make sure ZONE_NORMAL can be encoded to zero. So,
the compatibility can be guaranteed, such as GFP_KERNEL and GFP_ATOMIC
can be used as before.

Reserve __GFP_MOVABLE in bit 3, so that it can continue to be used as
a flag. Same as before, __GFP_MOVABLE respresents movable migrate type
for ZONE_DMA, ZONE_DMA32, and ZONE_NORMAL. But when it is enabled with
__GFP_HIGHMEM, ZONE_MOVABLE shall be returned instead of ZONE_HIGHMEM.
__GFP_ZONE_MOVABLE is created to realize it.

With this patch, just enabling __GFP_MOVABLE and __GFP_HIGHMEM is not
enough to get ZONE_MOVABLE from gfp_zone. All subsystems should use
GFP_HIGHUSER_MOVABLE directly to achieve that.

Decode zone number directly from bottom three bits of flags in gfp_zone.
The theory of encoding and decoding is,
A ^ B ^ B = A

Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Huaisheng Ye <yehs1@lenovo.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Christoph Hellwig <hch@infradead.org>
---
include/linux/gfp.h | 107 ++++++++++------------------------------------------
1 file changed, 20 insertions(+), 87 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 1a4582b..f76ccd76 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -16,9 +16,7 @@
*/

/* Plain integer GFP bitmasks. Do not use this directly. */
-#define ___GFP_DMA 0x01u
-#define ___GFP_HIGHMEM 0x02u
-#define ___GFP_DMA32 0x04u
+#define ___GFP_ZONE_MASK 0x07u
#define ___GFP_MOVABLE 0x08u
#define ___GFP_RECLAIMABLE 0x10u
#define ___GFP_HIGH 0x20u
@@ -53,11 +51,15 @@
* without the underscores and use them consistently. The definitions here may
* be used in bit comparisons.
*/
-#define __GFP_DMA ((__force gfp_t)___GFP_DMA)
-#define __GFP_HIGHMEM ((__force gfp_t)___GFP_HIGHMEM)
-#define __GFP_DMA32 ((__force gfp_t)___GFP_DMA32)
+#define __GFP_DMA ((__force gfp_t)OPT_ZONE_DMA ^ ZONE_NORMAL)
+#define __GFP_HIGHMEM ((__force gfp_t)OPT_ZONE_HIGHMEM ^ ZONE_NORMAL)
+#define __GFP_DMA32 ((__force gfp_t)OPT_ZONE_DMA32 ^ ZONE_NORMAL)
#define __GFP_MOVABLE ((__force gfp_t)___GFP_MOVABLE) /* ZONE_MOVABLE allowed */
-#define GFP_ZONEMASK (__GFP_DMA|__GFP_HIGHMEM|__GFP_DMA32|__GFP_MOVABLE)
+#define GFP_ZONEMASK ((__force gfp_t)___GFP_ZONE_MASK | ___GFP_MOVABLE)
+/* bottom 3 bits of GFP bitmasks are used for zone number encoded*/
+#define __GFP_ZONE_MASK ((__force gfp_t)___GFP_ZONE_MASK)
+#define __GFP_ZONE_MOVABLE \
+ ((__force gfp_t)(ZONE_MOVABLE ^ ZONE_NORMAL) | ___GFP_MOVABLE)

/*
* Page mobility and placement hints
@@ -268,6 +270,13 @@
* available and will not wake kswapd/kcompactd on failure. The _LIGHT
* version does not attempt reclaim/compaction at all and is by default used
* in page fault path, while the non-light is used by khugepaged.
+ *
+ * GFP_NORMAL() is used to clear bottom 3 bits of GFP bitmask. Actually it
+ * returns encoded ZONE_NORMAL bits.
+ *
+ * GFP_NORMAL_UNMOVABLE() is similar to GFP_NORMAL, but it clear bottom 4 bits
+ * of GFP bitmask. Excepting the encoded ZONE_NORMAL bits, it clears MOVABLE
+ * flags as well.
*/
#define GFP_ATOMIC (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM)
#define GFP_KERNEL (__GFP_RECLAIM | __GFP_IO | __GFP_FS)
@@ -279,10 +288,12 @@
#define GFP_DMA __GFP_DMA
#define GFP_DMA32 __GFP_DMA32
#define GFP_HIGHUSER (GFP_USER | __GFP_HIGHMEM)
-#define GFP_HIGHUSER_MOVABLE (GFP_HIGHUSER | __GFP_MOVABLE)
+#define GFP_HIGHUSER_MOVABLE (GFP_USER | __GFP_ZONE_MOVABLE)
#define GFP_TRANSHUGE_LIGHT ((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
__GFP_NOMEMALLOC | __GFP_NOWARN) & ~__GFP_RECLAIM)
#define GFP_TRANSHUGE (GFP_TRANSHUGE_LIGHT | __GFP_DIRECT_RECLAIM)
+#define GFP_NORMAL(gfp) ((gfp) & ~__GFP_ZONE_MASK)
+#define GFP_NORMAL_UNMOVABLE(gfp) ((gfp) & ~GFP_ZONEMASK)

/* Convert GFP flags to their corresponding migrate type */
#define GFP_MOVABLE_MASK (__GFP_RECLAIMABLE|__GFP_MOVABLE)
@@ -326,87 +337,9 @@ static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags)
#define OPT_ZONE_DMA32 ZONE_NORMAL
#endif

-/*
- * GFP_ZONE_TABLE is a word size bitstring that is used for looking up the
- * zone to use given the lowest 4 bits of gfp_t. Entries are GFP_ZONES_SHIFT
- * bits long and there are 16 of them to cover all possible combinations of
- * __GFP_DMA, __GFP_DMA32, __GFP_MOVABLE and __GFP_HIGHMEM.
- *
- * The zone fallback order is MOVABLE=>HIGHMEM=>NORMAL=>DMA32=>DMA.
- * But GFP_MOVABLE is not only a zone specifier but also an allocation
- * policy. Therefore __GFP_MOVABLE plus another zone selector is valid.
- * Only 1 bit of the lowest 3 bits (DMA,DMA32,HIGHMEM) can be set to "1".
- *
- * bit result
- * =================
- * 0x0 => NORMAL
- * 0x1 => DMA or NORMAL
- * 0x2 => HIGHMEM or NORMAL
- * 0x3 => BAD (DMA+HIGHMEM)
- * 0x4 => DMA32 or DMA or NORMAL
- * 0x5 => BAD (DMA+DMA32)
- * 0x6 => BAD (HIGHMEM+DMA32)
- * 0x7 => BAD (HIGHMEM+DMA32+DMA)
- * 0x8 => NORMAL (MOVABLE+0)
- * 0x9 => DMA or NORMAL (MOVABLE+DMA)
- * 0xa => MOVABLE (Movable is valid only if HIGHMEM is set too)
- * 0xb => BAD (MOVABLE+HIGHMEM+DMA)
- * 0xc => DMA32 (MOVABLE+DMA32)
- * 0xd => BAD (MOVABLE+DMA32+DMA)
- * 0xe => BAD (MOVABLE+DMA32+HIGHMEM)
- * 0xf => BAD (MOVABLE+DMA32+HIGHMEM+DMA)
- *
- * GFP_ZONES_SHIFT must be <= 2 on 32 bit platforms.
- */
-
-#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 * 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)\
-)
-
-/*
- * GFP_ZONE_BAD is a bitmap for all combinations of __GFP_DMA, __GFP_DMA32
- * __GFP_HIGHMEM and __GFP_MOVABLE that are not permitted. One flag per
- * entry starting with bit 0. Bit is set if the combination is not
- * allowed.
- */
-#define GFP_ZONE_BAD ( \
- 1 << (___GFP_DMA | ___GFP_HIGHMEM) \
- | 1 << (___GFP_DMA | ___GFP_DMA32) \
- | 1 << (___GFP_DMA32 | ___GFP_HIGHMEM) \
- | 1 << (___GFP_DMA | ___GFP_DMA32 | ___GFP_HIGHMEM) \
- | 1 << (___GFP_MOVABLE | ___GFP_HIGHMEM | ___GFP_DMA) \
- | 1 << (___GFP_MOVABLE | ___GFP_DMA32 | ___GFP_DMA) \
- | 1 << (___GFP_MOVABLE | ___GFP_DMA32 | ___GFP_HIGHMEM) \
- | 1 << (___GFP_MOVABLE | ___GFP_DMA32 | ___GFP_DMA | ___GFP_HIGHMEM) \
-)
-
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 * GFP_ZONES_SHIFT)) &
- ((1 << GFP_ZONES_SHIFT) - 1);
- VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
- return z;
+ return ((__force unsigned int)flags & __GFP_ZONE_MASK) ^ ZONE_NORMAL;
}

/*
--
1.8.3.1
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