region_count

/*
 * Count and return the number of huge pages in the reserve map
 * that intersect with the range [f, t).
 */
static long region_count(struct resv_map *resv, long f, long t)
{
    struct list_head *head = &resv->regions;
    struct file_region *rg;
    long chg = 0;
 
    spin_lock(&resv->lock);
    /* Locate each segment we overlap with, and count that overlap. */
    list_for_each_entry(rg, head, link) {
        long seg_from;
        long seg_to;
 
        if (rg->to <= f)
            continue;
        if (rg->from >= t)
            break;
 
        seg_from = max(rg->from, f);
        seg_to = min(rg->to, t);
 
        chg += seg_to - seg_from;
    }
    spin_unlock(&resv->lock);
 
    return chg;
}
函数源码
