find_next_to

/*
 * Scan swap_map (or frontswap_map if frontswap parameter is true)
 * from current position to next entry still in use. Return 0
 * if there are no inuse entries after prev till end of the map.
 */
static unsigned int find_next_to_unuse(struct swap_info_struct *si,
                    unsigned int prev, bool frontswap)
{
    unsigned int i;
    unsigned char count;
 
    /*
     * No need for swap_lock here: we're just looking
     * for whether an entry is in use, not modifying it; false
     * hits are okay, and sys_swapoff() has already prevented new
     * allocations from this area (while holding swap_lock).
     */
    for (i = prev + 1; i < si->max; i++) {
        count = READ_ONCE(si->swap_map[i]);
        if (count && swap_count(count) != SWAP_MAP_BAD)
            if (!frontswap || frontswap_test(si, i))
                break;
        if ((i % LATENCY_LIMIT) == 0)
            cond_resched();
    }
 
    if (i == si->max)
        i = 0;
 
    return i;
}
函数源码
