rust重构mmio_buddy和mmio #178
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fslongjin
requested changes
Mar 1, 2023
fslongjin
reviewed
Mar 4, 2023
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|   `free_regions`的下标（index）与内存块的大小有关。由于每个内存块大小都为$2^{n}$ bit，那么可以令$exp = n$。index与exp的换算公式如下：$index = exp - 12$。e.g. 一个大小为$2^{12}$ bit的内存块，其$exp = 12$，使用上述公式计算得$index = 12 -12 = 0$，所以该内存块会被存入`free_regions[0].list`中。通过上述换算公式，每次取出或释放$2^n$大小的内存块，只需要操作`free_regions[n -12]`即可。DragonOS中，buddy内存池最大的内存块大小为$1G = 2^{30}bit$，最小的内存块大小为 $4K = 2^{12} bit$，所以$index\in[0,18]$。 | ||
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|   作为内存分配机制，buddy服务于所有进程，为了解决在各个进程之间实现free_regions中的链表数据同步的问题，`free_regions`中的链表类型采用加了[自旋锁 — DragonOS dev 文档](https://docs.dragonos.org/zh_CN/latest/kernel/locking/spinlock.html#spinlock)（SpinLock）的空闲内存块链表（MmioFreeRegionList），`MmioFreeRegionList`中封装有真正的存储了空闲内存块信息的结构体的链表（list）和对应链表长度（num_free）。有了自选锁后，同一时刻只允许一个进程修改某个链表，如取出链表元素（申请内存）或者向链表中插入元素（释放内存）。 |
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