redis源码分析[03]-内存管理-zmalloc.c

最新推荐文章于 2020-06-15 14:03:08 发布

原创最新推荐文章于 2020-06-15 14:03:08 发布 · 250 阅读

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#redis源码分析

redis在每一块用到内存地址前面增加了一个字的内存，用来保存内存的大小

//定义一个字的长度
#if defined(__sun) || defined(__sparc) || defined(__sparc__)
#define PREFIX_SIZE (sizeof(long long))
#else
#define PREFIX_SIZE (sizeof(size_t))
#endif

原子操作，给一个变量增加或减少__n

#define update_zmalloc_stat_add(__n) __sync_add_and_fetch(&used_memory, (__n))
#define update_zmalloc_stat_sub(__n) __sync_sub_and_fetch(&used_memory, (__n))

//为了统计当前内存的使用量，每申请一块内存就会记录申请的大小
#define update_zmalloc_stat_alloc(__n) do { \
    size_t _n = (__n); \
    /*malloc()本身能够保证所分配的内存是8字节对齐的：如果你要分配的内存不是8的倍数，那么malloc
就会多分配一点，来凑成8的倍数。所以update_zmalloc_stat_alloc函数（或者说zmalloc()相对malloc()
而言）真正要实现的功能并不是进行8字节对齐（malloc已经保证了），它的真正目的是使变量used_memory精
确的维护实际已分配内存的大小。*/
    if (_n&(sizeof(long)-1)) _n += sizeof(long)-(_n&(sizeof(long)-1)); \
    if (zmalloc_thread_safe) { \
        update_zmalloc_stat_add(_n); \
    } else { \
        used_memory += _n; \
    } \
} while(0)
//为了统计当前内存的使用量，每释放一块内存就会记录释放的大小
#define update_zmalloc_stat_free(__n) do { \
    size_t _n = (__n); \
    //内存对齐
    if (_n&(sizeof(long)-1)) _n += sizeof(long)-(_n&(sizeof(long)-1)); \
    if (zmalloc_thread_safe) { \
        update_zmalloc_stat_sub(_n); \
    } else { \
        used_memory -= _n; \
    } \
} while(0)

static size_t used_memory = 0;//用来统计内存的使用量
static int zmalloc_thread_safe = 0;//内存申请是否是线程安全的
pthread_mutex_t used_memory_mutex = PTHREAD_MUTEX_INITIALIZER;//记录内存使用量使用的锁

//内存申请失败时执行的默认方法
static void zmalloc_default_oom(size_t size) {
    fprintf(stderr, "zmalloc: Out of memory trying to allocate %zu bytes\n",
        size);
    fflush(stderr);
    abort();
}

static void (*zmalloc_oom_handler)(size_t) = zmalloc_default_oom;
//申请内存
void *zmalloc(size_t size) {
    void *ptr = malloc(size+PREFIX_SIZE);//在申请量size的基础上增加一个字的大小

    if (!ptr) zmalloc_oom_handler(size);
#ifdef HAVE_MALLOC_SIZE
    update_zmalloc_stat_alloc(zmalloc_size(ptr));
    return ptr;
#else
    *((size_t*)ptr) = size;//用来记录这块内存的大小
    update_zmalloc_stat_alloc(size+PREFIX_SIZE);//更新内存使用总量
    return (char*)ptr+PREFIX_SIZE;//返回可用的内存首地址指针
#endif
}

void *zcalloc(size_t size) {
    void *ptr = calloc(1, size+PREFIX_SIZE);//在申请量size的基础上增加一个字的大小,并置内存为0

    if (!ptr) zmalloc_oom_handler(size);
#ifdef HAVE_MALLOC_SIZE
    update_zmalloc_stat_alloc(zmalloc_size(ptr));
    return ptr;
#else
    *((size_t*)ptr) = size;
    update_zmalloc_stat_alloc(size+PREFIX_SIZE);//更新内存使用总量
    return (char*)ptr+PREFIX_SIZE;
#endif
}
//重新申请内存
void *zrealloc(void *ptr, size_t size) {
#ifndef HAVE_MALLOC_SIZE
    void *realptr;
#endif
    size_t oldsize;
    void *newptr;

    if (ptr == NULL) return zmalloc(size);
#ifdef HAVE_MALLOC_SIZE
    oldsize = zmalloc_size(ptr);
    newptr = realloc(ptr,size);
    if (!newptr) zmalloc_oom_handler(size);

    update_zmalloc_stat_free(oldsize);
    update_zmalloc_stat_alloc(zmalloc_size(newptr));
    return newptr;
#else
    realptr = (char*)ptr-PREFIX_SIZE;//找到实际申请的内存首地址
    oldsize = *((size_t*)realptr);//旧内存的大小
    newptr = realloc(realptr,size+PREFIX_SIZE);//申请新内存
    if (!newptr) zmalloc_oom_handler(size);

    *((size_t*)newptr) = size;//标记当前内存的大小
    update_zmalloc_stat_free(oldsize);//更新内存：减少旧内存的大小
    update_zmalloc_stat_alloc(size);//更新内存：增加新内存的大小
    return (char*)newptr+PREFIX_SIZE;//返回可用的内存首地址指针
#endif
}

//检测一个内存块的大小
#ifndef HAVE_MALLOC_SIZE
size_t zmalloc_size(void *ptr) {
    void *realptr = (char*)ptr-PREFIX_SIZE;//找到原始内存地址
    size_t size = *((size_t*)realptr);//实际可用内存的大小
    //内存对齐
    if (size&(sizeof(long)-1)) size += sizeof(long)-(size&(sizeof(long)-1));
    return size+PREFIX_SIZE;//实际申请的内存大小
}
#endif
//释放内存
void zfree(void *ptr) {
#ifndef HAVE_MALLOC_SIZE
    void *realptr;
    size_t oldsize;
#endif

    if (ptr == NULL) return;
#ifdef HAVE_MALLOC_SIZE
    update_zmalloc_stat_free(zmalloc_size(ptr));
    free(ptr);
#else
    realptr = (char*)ptr-PREFIX_SIZE;
    oldsize = *((size_t*)realptr);
    update_zmalloc_stat_free(oldsize+PREFIX_SIZE);//更新内存使用总量
    free(realptr);
#endif
}
//复制一份内存
char *zstrdup(const char *s) {
    size_t l = strlen(s)+1;
    char *p = zmalloc(l);

    memcpy(p,s,l);
    return p;
}
//获取当前所用内存总量
size_t zmalloc_used_memory(void) {
    size_t um;

    if (zmalloc_thread_safe) {
#if defined(__ATOMIC_RELAXED) || defined(HAVE_ATOMIC)
        um = update_zmalloc_stat_add(0);//通过原子操作算出内存总量
#else
        pthread_mutex_lock(&used_memory_mutex);
        um = used_memory;
        pthread_mutex_unlock(&used_memory_mutex);
#endif
    }
    else {
        um = used_memory;
    }

    return um;
}
//设置内存使用为线程安全
void zmalloc_enable_thread_safeness(void) {
    zmalloc_thread_safe = 1;
}
//设置内存申请失败时触发的方法
void zmalloc_set_oom_handler(void (*oom_handler)(size_t)) {
    zmalloc_oom_handler = oom_handler;
}

#if defined(HAVE_PROC_STAT)
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

size_t zmalloc_get_rss(void) {
    int page = sysconf(_SC_PAGESIZE);
    size_t rss;
    char buf[4096];
    char filename[256];
    int fd, count;
    char *p, *x;

    snprintf(filename,256,"/proc/%d/stat",getpid());
    if ((fd = open(filename,O_RDONLY)) == -1) return 0;
    if (read(fd,buf,4096) <= 0) {
        close(fd);
        return 0;
    }
    close(fd);

    p = buf;
    count = 23; /* RSS is the 24th field in /proc/<pid>/stat */
    while(p && count--) {
        p = strchr(p,' ');
        if (p) p++;
    }
    if (!p) return 0;
    x = strchr(p,' ');
    if (!x) return 0;
    *x = '\0';

    rss = strtoll(p,NULL,10);
    rss *= page;
    return rss;
}
#elif defined(HAVE_TASKINFO)
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/sysctl.h>
#include <mach/task.h>
#include <mach/mach_init.h>

size_t zmalloc_get_rss(void) {
    task_t task = MACH_PORT_NULL;
    struct task_basic_info t_info;
    mach_msg_type_number_t t_info_count = TASK_BASIC_INFO_COUNT;

    if (task_for_pid(current_task(), getpid(), &task) != KERN_SUCCESS)
        return 0;
    task_info(task, TASK_BASIC_INFO, (task_info_t)&t_info, &t_info_count);

    return t_info.resident_size;
}
#else
//获取当前进程实际所驻留在内存中的空间大小
size_t zmalloc_get_rss(void) {
    /* If we can't get the RSS in an OS-specific way for this system just
     * return the memory usage we estimated in zmalloc()..
     *
     * Fragmentation will appear to be always 1 (no fragmentation)
     * of course... */
    return zmalloc_used_memory();
}
#endif

//获取内存碎片率 驻留在内存中的空间大小/分配出去的内存大小
float zmalloc_get_fragmentation_ratio(size_t rss) {
    return (float)rss/zmalloc_used_memory();
}

/* Get the sum of the specified field (converted form kb to bytes) in
 * /proc/self/smaps. The field must be specified with trailing ":" as it
 * apperas in the smaps output.
 *
 * Example: zmalloc_get_smap_bytes_by_field("Rss:");
 */
#if defined(HAVE_PROC_SMAPS)
size_t zmalloc_get_smap_bytes_by_field(char *field) {
    char line[1024];
    size_t bytes = 0;
    FILE *fp = fopen("/proc/self/smaps","r");
    int flen = strlen(field);

    if (!fp) return 0;
    while(fgets(line,sizeof(line),fp) != NULL) {
        if (strncmp(line,field,flen) == 0) {
            char *p = strchr(line,'k');
            if (p) {
                *p = '\0';
                bytes += strtol(line+flen,NULL,10) * 1024;
            }
        }
    }
    fclose(fp);
    return bytes;
}
#else
size_t zmalloc_get_smap_bytes_by_field(char *field) {
    ((void) field);
    return 0;
}
#endif

size_t zmalloc_get_private_dirty(void) {
    return zmalloc_get_smap_bytes_by_field("Private_Dirty:");
}

//获取物理内存大小
size_t zmalloc_get_memory_size(void) {
#if defined(__unix__) || defined(__unix) || defined(unix) || \
    (defined(__APPLE__) && defined(__MACH__))
#if defined(CTL_HW) && (defined(HW_MEMSIZE) || defined(HW_PHYSMEM64))
    int mib[2];
    mib[0] = CTL_HW;
#if defined(HW_MEMSIZE)
    mib[1] = HW_MEMSIZE;            /* OSX. --------------------- */
#elif defined(HW_PHYSMEM64)
    mib[1] = HW_PHYSMEM64;          /* NetBSD, OpenBSD. --------- */
#endif
    int64_t size = 0;               /* 64-bit */
    size_t len = sizeof(size);
    if (sysctl( mib, 2, &size, &len, NULL, 0) == 0)
        return (size_t)size;
    return 0L;          /* Failed? */

#elif defined(_SC_PHYS_PAGES) && defined(_SC_PAGESIZE)
    /* 我的centos用的是这个 页数*页大小 */
    return (size_t)sysconf(_SC_PHYS_PAGES) * (size_t)sysconf(_SC_PAGESIZE);

#elif defined(CTL_HW) && (defined(HW_PHYSMEM) || defined(HW_REALMEM))
    /* DragonFly BSD, FreeBSD, NetBSD, OpenBSD, and OSX. -------- */
    int mib[2];
    mib[0] = CTL_HW;
#if defined(HW_REALMEM)
    mib[1] = HW_REALMEM;        /* FreeBSD. ----------------- */
#elif defined(HW_PYSMEM)
    mib[1] = HW_PHYSMEM;        /* Others. ------------------ */
#endif
    unsigned int size = 0;      /* 32-bit */
    size_t len = sizeof(size);
    if (sysctl(mib, 2, &size, &len, NULL, 0) == 0)
        return (size_t)size;
    return 0L;          /* Failed? */
#endif /* sysctl and sysconf variants */

#else
    return 0L;          /* Unknown OS. */
#endif
}