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Subject[patch 02/41] cpu alloc: The allocator
The per cpu allocator allows dynamic allocation of memory on all
processors simultaneously. A bitmap is used to track used areas.
The allocator implements tight packing to reduce the cache footprint
and increase speed since cacheline contention is typically not a concern
for memory mainly used by a single cpu. Small objects will fill up gaps
left by larger allocations that required alignments.

The size of the cpu_alloc area can be changed via make menuconfig.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
include/linux/percpu.h | 46 +++++++++++++
include/linux/vmstat.h | 2
mm/Kconfig | 6 +
mm/Makefile | 2
mm/cpu_alloc.c | 167 +++++++++++++++++++++++++++++++++++++++++++++++++
mm/vmstat.c | 1
6 files changed, 222 insertions(+), 2 deletions(-)
Index: linux-2.6/include/linux/vmstat.h
===================================================================
--- linux-2.6.orig/include/linux/vmstat.h 2008-05-29 19:41:21.000000000 -0700
+++ linux-2.6/include/linux/vmstat.h 2008-05-29 20:15:37.000000000 -0700
@@ -37,7 +37,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PS
FOR_ALL_ZONES(PGSCAN_KSWAPD),
FOR_ALL_ZONES(PGSCAN_DIRECT),
PGINODESTEAL, SLABS_SCANNED, KSWAPD_STEAL, KSWAPD_INODESTEAL,
- PAGEOUTRUN, ALLOCSTALL, PGROTATED,
+ PAGEOUTRUN, ALLOCSTALL, PGROTATED, CPU_BYTES,
#ifdef CONFIG_HUGETLB_PAGE
HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL,
#endif
Index: linux-2.6/mm/Kconfig
===================================================================
--- linux-2.6.orig/mm/Kconfig 2008-05-29 19:41:21.000000000 -0700
+++ linux-2.6/mm/Kconfig 2008-05-29 20:13:39.000000000 -0700
@@ -205,3 +205,9 @@ config NR_QUICK
config VIRT_TO_BUS
def_bool y
depends on !ARCH_NO_VIRT_TO_BUS
+
+config CPU_ALLOC_SIZE
+ int "Size of cpu alloc area"
+ default "30000"
+ help
+ Sets the maximum amount of memory that can be allocated via cpu_alloc
Index: linux-2.6/mm/Makefile
===================================================================
--- linux-2.6.orig/mm/Makefile 2008-05-29 19:41:21.000000000 -0700
+++ linux-2.6/mm/Makefile 2008-05-29 20:15:41.000000000 -0700
@@ -11,7 +11,7 @@ obj-y := bootmem.o filemap.o mempool.o
maccess.o page_alloc.o page-writeback.o pdflush.o \
readahead.o swap.o truncate.o vmscan.o \
prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
- page_isolation.o $(mmu-y)
+ page_isolation.o cpu_alloc.o $(mmu-y)

obj-$(CONFIG_PROC_PAGE_MONITOR) += pagewalk.o
obj-$(CONFIG_BOUNCE) += bounce.o
Index: linux-2.6/mm/cpu_alloc.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/mm/cpu_alloc.c 2008-05-29 20:13:39.000000000 -0700
@@ -0,0 +1,167 @@
+/*
+ * Cpu allocator - Manage objects allocated for each processor
+ *
+ * (C) 2008 SGI, Christoph Lameter <clameter@sgi.com>
+ * Basic implementation with allocation and free from a dedicated per
+ * cpu area.
+ *
+ * The per cpu allocator allows dynamic allocation of memory on all
+ * processor simultaneously. A bitmap is used to track used areas.
+ * The allocator implements tight packing to reduce the cache footprint
+ * and increase speed since cacheline contention is typically not a concern
+ * for memory mainly used by a single cpu. Small objects will fill up gaps
+ * left by larger allocations that required alignments.
+ */
+#include <linux/mm.h>
+#include <linux/mmzone.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/bitmap.h>
+#include <asm/sections.h>
+
+/*
+ * Basic allocation unit. A bit map is created to track the use of each
+ * UNIT_SIZE element in the cpu area.
+ */
+#define UNIT_TYPE int
+#define UNIT_SIZE sizeof(UNIT_TYPE)
+#define UNITS (CONFIG_CPU_ALLOC_SIZE / UNIT_SIZE)
+
+static DEFINE_PER_CPU(UNIT_TYPE, area[UNITS]);
+
+/*
+ * How many units are needed for an object of a given size
+ */
+static int size_to_units(unsigned long size)
+{
+ return DIV_ROUND_UP(size, UNIT_SIZE);
+}
+
+/*
+ * Lock to protect the bitmap and the meta data for the cpu allocator.
+ */
+static DEFINE_SPINLOCK(cpu_alloc_map_lock);
+static DECLARE_BITMAP(cpu_alloc_map, UNITS);
+static int first_free; /* First known free unit */
+
+/*
+ * Mark an object as used in the cpu_alloc_map
+ *
+ * Must hold cpu_alloc_map_lock
+ */
+static void set_map(int start, int length)
+{
+ while (length-- > 0)
+ __set_bit(start++, cpu_alloc_map);
+}
+
+/*
+ * Mark an area as freed.
+ *
+ * Must hold cpu_alloc_map_lock
+ */
+static void clear_map(int start, int length)
+{
+ while (length-- > 0)
+ __clear_bit(start++, cpu_alloc_map);
+}
+
+/*
+ * Allocate an object of a certain size
+ *
+ * Returns a special pointer that can be used with CPU_PTR to find the
+ * address of the object for a certain cpu.
+ */
+void *cpu_alloc(unsigned long size, gfp_t gfpflags, unsigned long align)
+{
+ unsigned long start;
+ int units = size_to_units(size);
+ void *ptr;
+ int first;
+ unsigned long flags;
+
+ if (!size)
+ return ZERO_SIZE_PTR;
+
+ spin_lock_irqsave(&cpu_alloc_map_lock, flags);
+
+ first = 1;
+ start = first_free;
+
+ for ( ; ; ) {
+
+ start = find_next_zero_bit(cpu_alloc_map, UNITS, start);
+ if (start >= UNITS)
+ goto out_of_memory;
+
+ if (first)
+ first_free = start;
+
+ /*
+ * Check alignment and that there is enough space after
+ * the starting unit.
+ */
+ if (start % (align / UNIT_SIZE) == 0 &&
+ find_next_bit(cpu_alloc_map, UNITS, start + 1)
+ >= start + units)
+ break;
+ start++;
+ first = 0;
+ }
+
+ if (first)
+ first_free = start + units;
+
+ if (start + units > UNITS)
+ goto out_of_memory;
+
+ set_map(start, units);
+ __count_vm_events(CPU_BYTES, units * UNIT_SIZE);
+
+ spin_unlock_irqrestore(&cpu_alloc_map_lock, flags);
+
+ ptr = per_cpu_var(area) + start;
+
+ if (gfpflags & __GFP_ZERO) {
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ memset(CPU_PTR(ptr, cpu), 0, size);
+ }
+
+ return ptr;
+
+out_of_memory:
+ spin_unlock_irqrestore(&cpu_alloc_map_lock, flags);
+ return NULL;
+}
+EXPORT_SYMBOL(cpu_alloc);
+
+/*
+ * Free an object. The pointer must be a cpu pointer allocated
+ * via cpu_alloc.
+ */
+void cpu_free(void *start, unsigned long size)
+{
+ unsigned long units = size_to_units(size);
+ unsigned long index = (int *)start - per_cpu_var(area);
+ unsigned long flags;
+
+ if (!start || start == ZERO_SIZE_PTR)
+ return;
+
+ BUG_ON(index >= UNITS ||
+ !test_bit(index, cpu_alloc_map) ||
+ !test_bit(index + units - 1, cpu_alloc_map));
+
+ spin_lock_irqsave(&cpu_alloc_map_lock, flags);
+
+ clear_map(index, units);
+ __count_vm_events(CPU_BYTES, -units * UNIT_SIZE);
+
+ if (index < first_free)
+ first_free = index;
+
+ spin_unlock_irqrestore(&cpu_alloc_map_lock, flags);
+}
+EXPORT_SYMBOL(cpu_free);
Index: linux-2.6/mm/vmstat.c
===================================================================
--- linux-2.6.orig/mm/vmstat.c 2008-05-29 19:41:21.000000000 -0700
+++ linux-2.6/mm/vmstat.c 2008-05-29 20:13:39.000000000 -0700
@@ -653,6 +653,7 @@ static const char * const vmstat_text[]
"allocstall",

"pgrotated",
+ "cpu_bytes",
#ifdef CONFIG_HUGETLB_PAGE
"htlb_buddy_alloc_success",
"htlb_buddy_alloc_fail",
Index: linux-2.6/include/linux/percpu.h
===================================================================
--- linux-2.6.orig/include/linux/percpu.h 2008-05-29 19:41:21.000000000 -0700
+++ linux-2.6/include/linux/percpu.h 2008-05-29 20:29:12.000000000 -0700
@@ -135,4 +135,50 @@ static inline void percpu_free(void *__p
#define free_percpu(ptr) percpu_free((ptr))
#define per_cpu_ptr(ptr, cpu) percpu_ptr((ptr), (cpu))

+
+/*
+ * cpu allocator definitions
+ *
+ * The cpu allocator allows allocating an instance of an object for each
+ * processor and the use of a single pointer to access all instances
+ * of the object. cpu_alloc provides optimized means for accessing the
+ * instance of the object belonging to the currently executing processor
+ * as well as special atomic operations on fields of objects of the
+ * currently executing processor.
+ *
+ * Cpu objects are typically small. The allocator packs them tightly
+ * to increase the chance on each access that a per cpu object is already
+ * cached. Alignments may be specified but the intent is to align the data
+ * properly due to cpu alignment constraints and not to avoid cacheline
+ * contention. Any holes left by aligning objects are filled up with smaller
+ * objects that are allocated later.
+ *
+ * Cpu data can be allocated using CPU_ALLOC. The resulting pointer is
+ * pointing to the instance of the variable in the per cpu area provided
+ * by the loader. It is generally an error to use the pointer directly
+ * unless we are booting the system.
+ *
+ * __GFP_ZERO may be passed as a flag to zero the allocated memory.
+ */
+
+/* Return a pointer to the instance of a object for a particular processor */
+#define CPU_PTR(__p, __cpu) SHIFT_PERCPU_PTR((__p), per_cpu_offset(__cpu))
+
+/*
+ * Return a pointer to the instance of the object belonging to the processor
+ * running the current code.
+ */
+#define THIS_CPU(__p) SHIFT_PERCPU_PTR((__p), my_cpu_offset)
+#define __THIS_CPU(__p) SHIFT_PERCPU_PTR((__p), __my_cpu_offset)
+
+#define CPU_ALLOC(type, flags) ((typeof(type) *)cpu_alloc(sizeof(type), \
+ (flags), __alignof__(type)))
+#define CPU_FREE(pointer) cpu_free((pointer), sizeof(*(pointer)))
+
+/*
+ * Raw calls
+ */
+void *cpu_alloc(unsigned long size, gfp_t flags, unsigned long align);
+void cpu_free(void *cpu_pointer, unsigned long size);
+
#endif /* __LINUX_PERCPU_H */
--


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