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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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