内存管理-31-每进程内存统计-5-/proc/pid/maps

一、简介

1. 打印内容

8295:/ # cat /proc/584/maps
62217e2000-62218e8000 r--p 00000000 fc:00 166440964                      /system/bin/surfaceflinger
62218e8000-6221d75000 r-xp 00106000 fc:00 166440964                      /system/bin/surfaceflinger
6221d75000-6221da4000 r--p 00593000 fc:00 166440964                      /system/bin/surfaceflinger
6221da4000-6221dae000 rw-p 005c1000 fc:00 166440964                      /system/bin/surfaceflinger
6221dae000-6221db0000 rw-p 00000000 00:00 0                              [anon:.bss]
73bb942000-73bba02000 rw-s 00000000 00:0a 23087                          /dmabuf:
73c9b80000-73c9f00000 rw-p 00000000 00:00 0                              [anon:libc_malloc]
73cc064000-73cc067000 r--p 00000000 fc:01 15551301                       /vendor/lib64/libvmmem.so
73cc067000-73cc06a000 r-xp 00003000 fc:01 15551301                       /vendor/lib64/libvmmem.so
73cc06a000-73cc06b000 r--p 00006000 fc:01 15551301                       /vendor/lib64/libvmmem.so
73ce892000-73ce894000 rw-p 00000000 00:00 0
745740f000-7457417000 rw-p 00000000 00:00 0                              [anon:thread signal stack]
7458396000-74583b6000 r--s 00000000 00:14 17021                          /dev/__properties__/u:object_r:system_prop:s0
7459c83000-7459c84000 r--p 00000000 00:00 0                              [vvar]
7459c84000-7459c85000 r-xp 00000000 00:00 0                              [vdso] //匿名页且vma->mm=NULL
...
7fd688f000-7fd68b0000 rw-p 00000000 00:00 0                              [stack] //vma地址落在栈区间内，通常位于最后

每行对应一个 vm_area_struct 结构的打印，打印内容：

(1) 对于文件映射VMA

62218e8000-6221d75000: vma->vm_start - vma->vm_end 
r-xp: vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_MAYSHARE)? 'r''w''x''s' : '-''-''-''p';
00106000: vma->vm_pgoff << PAGE_SHIFT;
fc:00: MAJOR(inode->i_sb->s_dev):MINOR(inode->i_sb->s_dev);
166440964: inode->i_ino

(2) 对于匿名VMA

6221dae000-6221db0000: vma->vm_start - vma->vm_end 
rw-p: vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_MAYSHARE)? 'r''w''x''s' : '-''-''-''p';
00000000: 固定为0
00:00: 固定为0:0
0: 固定为0

二、代码实现

1. 代码路径

static const struct pid_entry tgid_base_stuff[] = { //fs/proc/base.c
    REG("maps",       S_IRUGO, proc_pid_maps_operations),
};

static const struct pid_entry tid_base_stuff[] = { //fs/proc/base.c
    REG("maps",      S_IRUGO, proc_pid_maps_operations),
}

proc_pid_maps_operations.pid_maps_open //base.c
    proc_pid_maps_op.show_map //task_mmu.c
        show_map_vma //task_mmu.c
        m_cache_vma //task_mmu.c 与打印无关

2. 打印函数

static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma) //task_mmu.c
{
    struct mm_struct *mm = vma->vm_mm;
    struct file *file = vma->vm_file;
    vm_flags_t flags = vma->vm_flags;
    unsigned long ino = 0;
    unsigned long long pgoff = 0;
    unsigned long start, end;
    dev_t dev = 0;
    const char *name = NULL;

    /* 若是文件映射对应的vma */
    if (file) {
        struct inode *inode = file_inode(vma->vm_file); //return f->f_inode;
        dev = inode->i_sb->s_dev;
        ino = inode->i_ino;
        pgoff = ((loff_t)vma->vm_pgoff) << PAGE_SHIFT;
    }

    start = vma->vm_start;
    end = vma->vm_end;
    /*
     * show_map_vma: (m, vma->vm_start, vma->vm_end, vma->vm_flags, vma->vm_pgoff)
     * 文件映射: pgoff=vma->vm_pgoff, dev=inode->i_sb->s_dev; ino = inode->i_ino;
     * 匿名映射 pgoff=0; dev=0; ino=0
     *
     * 此函数打印如 “59e95d6000-59e961b000 r-xp 0002b000 fc:00 166573033”
    */
    show_vma_header_prefix(m, start, end, flags, pgoff, dev, ino);

    /*
     * Print the dentry name for named mappings, and a
     * special [heap] marker for the heap:
     */
    /* 对于文件映射，打印pathname, 如"/system/bin/toybox", 然后就goto退出了 */
    if (file) {
        seq_pad(m, ' ');
        seq_file_path(m, file, "\n");
        goto done;
    }

    /* 尝试通过vm_ops->name回调获取匿名映射VMA对应的名字 */
    if (vma->vm_ops && vma->vm_ops->name) {
        name = vma->vm_ops->name(vma);
        if (name)
            goto done;
    }

    /* _weak的，没定义，默认返回NULL */
    name = arch_vma_name(vma);
    if (!name) {
        /* 匿名VMA的vma->mm=NULL打印这个 */
        if (!mm) {
            name = "[vdso]";
            goto done;
        }
        /*
         * 若VMA地址与堆空间[start_brk, brk]相交，就认为是heap
         * 实测 cat maps | grep heap 基本上是没有的，brk的确被舍弃了
         */
        if (vma->vm_start <= mm->brk && vma->vm_end >= mm->start_brk) {
            name = "[heap]";
            goto done;
        }

        /* vma->vm_start <= mm->start_stack && vma->vm_end >= mm->start_stack 栈向下增长的 */
        if (is_stack(vma)) {
            name = "[stack]";
            goto done;
        }
        /* 若是文件映射直接返回NULL，若是匿名映射的VMA返回 vma->anon_name */
        if (vma_get_anon_name(vma)) {
            seq_pad(m, ' ');
            seq_print_vma_name(m, vma);
        }
    }

done:
    if (name) {
        seq_pad(m, ' ');
        seq_puts(m, name);
    }
    seq_putc(m, '\n');
}

static void show_vma_header_prefix(struct seq_file *m,
                   unsigned long start, unsigned long end,
                   vm_flags_t flags, unsigned long long pgoff,
                   dev_t dev, unsigned long ino)
{
    seq_setwidth(m, 25 + sizeof(void *) * 6 - 1);
    seq_put_hex_ll(m, NULL, start, 8);
    seq_put_hex_ll(m, "-", end, 8);
    seq_putc(m, ' ');
    seq_putc(m, flags & VM_READ ? 'r' : '-');
    seq_putc(m, flags & VM_WRITE ? 'w' : '-');
    seq_putc(m, flags & VM_EXEC ? 'x' : '-');
    seq_putc(m, flags & VM_MAYSHARE ? 's' : 'p');
    seq_put_hex_ll(m, " ", pgoff, 8);
    seq_put_hex_ll(m, " ", MAJOR(dev), 2);
    seq_put_hex_ll(m, ":", MINOR(dev), 2);
    seq_put_decimal_ull(m, " ", ino);
    seq_putc(m, ' ');
}