[PATCH] slab: allow arch override for kmem_bufctl_t

From: Manfred Spraul <manfred@colorfullife.com>

The slab allocator keeps track of the free objects in a slab with a linked
list of integers (typedef'ed to kmem_bufctl_t).  Right now unsigned int is
used for kmem_bufctl_t, i.e.  4 bytes per-object overhead.

The attached patch implements a per-arch definition of for this type:
Theoretically, unsigned short is sufficient for kmem_bufctl_t and this would
reduce the per-object overhead to 2 bytes.  But some archs cannot operate on
16-bit values efficiently, thus it's not possible to switch everyone to
ushort.

The chosen types are a result of dicussions with the various arch maintainers.

include/asm-alpha/types.h

@@ -56,6 +56,8 @@ typedef unsigned long u64;
 typedef u64 dma_addr_t;
 typedef u64 dma64_addr_t;
 
+typedef unsigned short kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 #endif /* __KERNEL__ */
 #endif /* _ALPHA_TYPES_H */

include/asm-arm/types.h

@@ -52,6 +52,8 @@ typedef unsigned long long u64;
 typedef u32 dma_addr_t;
 typedef u32 dma64_addr_t;
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-arm26/types.h

@@ -52,6 +52,8 @@ typedef unsigned long long u64;
 typedef u32 dma_addr_t;
 typedef u32 dma64_addr_t;
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-cris/types.h

@@ -51,6 +51,8 @@ typedef unsigned long long u64;
  
 typedef u32 dma_addr_t;
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-h8300/types.h

@@ -58,6 +58,8 @@ typedef u32 dma_addr_t;
 #define HAVE_SECTOR_T
 typedef u64 sector_t;
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASSEMBLY__ */

include/asm-i386/types.h

@@ -63,6 +63,8 @@ typedef u64 sector_t;
 #define HAVE_SECTOR_T
 #endif
 
+typedef unsigned short kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-ia64/types.h

@@ -67,6 +67,8 @@ typedef __u64 u64;
 
 typedef u64 dma_addr_t;
 
+typedef unsigned short kmem_bufctl_t;
+
 # endif /* __KERNEL__ */
 #endif /* !__ASSEMBLY__ */
 

include/asm-m68k/types.h

@@ -60,6 +60,8 @@ typedef unsigned long long u64;
 typedef u32 dma_addr_t;
 typedef u32 dma64_addr_t;
 
+typedef unsigned short kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-mips/types.h

@@ -99,6 +99,8 @@ typedef u64 sector_t;
 #define HAVE_SECTOR_T
 #endif
 
+typedef unsigned short kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-parisc/types.h

@@ -56,6 +56,8 @@ typedef unsigned long long u64;
 typedef u32 dma_addr_t;
 typedef u64 dma64_addr_t;
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-ppc/types.h

@@ -62,6 +62,8 @@ typedef u64 sector_t;
 #define HAVE_SECTOR_T
 #endif
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-ppc64/types.h

@@ -73,6 +73,8 @@ typedef struct {
 } func_descr_t;
 #endif /* __ASSEMBLY__ */
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* __KERNEL__ */
 
 #endif /* _PPC64_TYPES_H */

include/asm-s390/types.h

@@ -93,6 +93,8 @@ typedef u64 sector_t;
 #define HAVE_SECTOR_T
 #endif
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* ! __s390x__   */
 #endif /* __ASSEMBLY__  */
 #endif /* __KERNEL__    */

include/asm-sh/types.h

@@ -58,6 +58,8 @@ typedef u64 sector_t;
 #define HAVE_SECTOR_T
 #endif
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-sparc/types.h

@@ -54,6 +54,8 @@ typedef unsigned long long u64;
 typedef u32 dma_addr_t;
 typedef u32 dma64_addr_t;
 
+typedef unsigned short kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-sparc64/types.h

@@ -56,6 +56,8 @@ typedef unsigned long u64;
 typedef u32 dma_addr_t;
 typedef u64 dma64_addr_t;
 
+typedef unsigned short kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-v850/types.h

@@ -59,6 +59,8 @@ typedef unsigned long long u64;
 
 typedef u32 dma_addr_t;
 
+typedef unsigned int kmem_bufctl_t;
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

include/asm-x86_64/types.h

@@ -51,6 +51,8 @@ typedef u64 dma_addr_t;
 typedef u64 sector_t;
 #define HAVE_SECTOR_T
 
+typedef unsigned short kmem_bufctl_t;
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

mm/slab.c

@@ -161,10 +161,9 @@
  * is less than 512 (PAGE_SIZE<<3), but greater than 256.
  */
 
-#define BUFCTL_END	0xffffFFFF
-#define BUFCTL_FREE	0xffffFFFE
-#define	SLAB_LIMIT	0xffffFFFD
-typedef unsigned int kmem_bufctl_t;
+#define BUFCTL_END	(((kmem_bufctl_t)(~0U))-0)
+#define BUFCTL_FREE	(((kmem_bufctl_t)(~0U))-1)
+#define	SLAB_LIMIT	(((kmem_bufctl_t)(~0U))-2)
 
 /* Max number of objs-per-slab for caches which use off-slab slabs.
  * Needed to avoid a possible looping condition in cache_grow().