Messages in this thread Patch in this message | | | Date | Fri, 19 Sep 2008 10:58:09 +0300 | From | "Pekka Enberg" <> | Subject | Re: [patch 3/4] cpu alloc: The allocator |
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Hi Christoph,
On Fri, Sep 19, 2008 at 2:36 AM, Christoph Lameter <cl@linux-foundation.org> wrote: > 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 the percpu=xxx > kernel parameter. > > Signed-off-by: Christoph Lameter <cl@linux-foundation.org> > > --- > include/linux/percpu.h | 46 ++++++++++++ > include/linux/vmstat.h | 2 > mm/Makefile | 2 > mm/cpu_alloc.c | 181 +++++++++++++++++++++++++++++++++++++++++++++++++ > mm/vmstat.c | 1 > 5 files changed, 230 insertions(+), 2 deletions(-) > create mode 100644 include/linux/cpu_alloc.h > create mode 100644 mm/cpu_alloc.c > > Index: linux-2.6/include/linux/vmstat.h > =================================================================== > --- linux-2.6.orig/include/linux/vmstat.h 2008-09-16 18:13:44.000000000 -0700 > +++ linux-2.6/include/linux/vmstat.h 2008-09-16 18:30:24.000000000 -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/Makefile > =================================================================== > --- linux-2.6.orig/mm/Makefile 2008-09-16 18:13:44.000000000 -0700 > +++ linux-2.6/mm/Makefile 2008-09-16 18:30:24.000000000 -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 mm_init.o $(mmu-y) > + page_isolation.o mm_init.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 2008-09-16 19:04:09.000000000 -0700 > @@ -0,0 +1,177 @@ > +/* > + * Cpu allocator - Manage objects allocated for each processor > + * > + * (C) 2008 SGI, Christoph Lameter <clameter@sgi.com>
You probably want to drop that defunct email address.
> + * 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.
I found the first sentence a bit misleading. You can be easily fooled into thinking "simultaneously" means there's no global locking (well, I was).
> + * 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> > +#include <linux/bootmem.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) > + > +int units; /* Actual available 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 unsigned long *cpu_alloc_map; > +static int nr_units; /* Number of available 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, nr_units, start); > + if (start >= nr_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 &&
We probably want a:
if (WARN_ON(align == 0)) return NULL;
somewhere there at the beginning of the function to avoid division by zero.
> + find_next_bit(cpu_alloc_map, nr_units, start + 1) > + >= start + units) > + break; > + start++; > + first = 0; > + } > + > + if (first) > + first_free = start + units; > + > + if (start + units > nr_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_end + 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 - (int *)__per_cpu_end; > + unsigned long flags; > + > + if (!start || start == ZERO_SIZE_PTR) > + return; > + > + BUG_ON(index >= nr_units || > + !test_bit(index, cpu_alloc_map) || > + !test_bit(index + units - 1, cpu_alloc_map));
Why not turn this into three separate BUG_ON() calls? It's much easier to figure out the offending expression like that. Also, maybe we want these to be WARN_ON() calls (and early return) to avoid early boot panic?
> + > + 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); > + > + > +void cpu_alloc_init(void) > +{ > + nr_units = percpu_reserve / UNIT_SIZE; > + > + cpu_alloc_map = alloc_bootmem(BITS_TO_LONGS(nr_units)); > +} > + > Index: linux-2.6/mm/vmstat.c > =================================================================== > --- linux-2.6.orig/mm/vmstat.c 2008-09-16 18:13:44.000000000 -0700 > +++ linux-2.6/mm/vmstat.c 2008-09-16 18:30:24.000000000 -0700 > @@ -671,6 +671,7 @@ 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 2008-09-16 18:28:55.000000000 -0700 > +++ linux-2.6/include/linux/percpu.h 2008-09-16 19:05:39.000000000 -0700 > @@ -107,4 +107,52 @@ 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); > + > +void cpu_alloc_init(void); > + > #endif /* __LINUX_PERCPU_H */ > Index: linux-2.6/init/main.c > =================================================================== > --- linux-2.6.orig/init/main.c 2008-09-16 18:29:40.000000000 -0700 > +++ linux-2.6/init/main.c 2008-09-16 18:30:24.000000000 -0700 > @@ -368,7 +368,11 @@ static void __init smp_init(void) > #define smp_init() do { } while (0) > #endif > > -static inline void setup_per_cpu_areas(void) { } > +static inline void setup_per_cpu_areas(void) > +{ > + cpu_alloc_init(); > +} > + > static inline void setup_nr_cpu_ids(void) { } > static inline void smp_prepare_cpus(unsigned int maxcpus) { } > > @@ -405,6 +409,7 @@ static void __init setup_per_cpu_areas(v > char *ptr; > unsigned long nr_possible_cpus = num_possible_cpus(); > > + cpu_alloc_init(); > /* Copy section for each CPU (we discard the original) */ > size = ALIGN(PERCPU_AREA_SIZE, PAGE_SIZE); > printk(KERN_INFO "percpu area: %d bytes total, %d available.\n", > Index: linux-2.6/arch/x86/kernel/setup_percpu.c > =================================================================== > --- linux-2.6.orig/arch/x86/kernel/setup_percpu.c 2008-09-16 19:04:30.000000000 -0700 > +++ linux-2.6/arch/x86/kernel/setup_percpu.c 2008-09-16 19:04:48.000000000 -0700 > @@ -144,6 +144,7 @@ void __init setup_per_cpu_areas(void) > char *ptr; > int cpu; > > + cpu_alloc_init(); > /* Setup cpu_pda map */ > setup_cpu_pda_map();
We need to do sparc, powerpc, and ia64 too, right?
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