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<!doctype html>
<html lang="en">
<head>
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content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
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type="text/css">
<title>CSAPP 讨论会</title>
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<body class="d-flex flex-column h-100">
<div class="reveal">
<div class="slides">
<section>
<div class="center middle"><div style="width:100%"><div>
<h1 class=" text-2xl mt-2 font-sans">CSAPP 讨论会</h1>
<p class=" font-serif my-1">Week4 虚拟内存<br/>
2022/12/24</p>
</div>
</div>
</div>
</section>
<section>
<section> <div>
<h2 class=" text-xl mt-2 pb-2 font-sans">虚拟内存页表设计</h2>
<p class=" font-serif my-1">原理是维护一个虚拟内存到物理内存的映射</p>
<ul class=" list-disc font-serif">
<li class=" ml-8">哈希表</li>
<li class=" ml-8">多级固定页表(tree-based address translation)<ul class=" list-disc font-serif">
<li class=" ml-8">建立索引</li>
<li class=" ml-8">建立索引的索引</li>
<li class=" ml-8"><a href="https://www.kernel.org/doc/html/latest/admin-guide/mm/hugetlbpage.html">huge pages</a> (2MB, 1G)</li>
</ul>
</li>
</ul>
<p class=" font-serif my-1">查找过程(P.41)</p>
<ul class=" list-disc font-serif">
<li class=" ml-8">page table walk</li>
</ul>
</div> </section>
<section> <div>
<h2 class=" text-xl mt-2 pb-2 font-sans">cache</h2>
<ul class=" list-disc font-serif">
<li class=" ml-8">TLB</li>
<li class=" ml-8">L1, L2, L3</li>
</ul>
<div class="codehilite"><pre class=" bg-gray-100 overflow-x-auto rounded p-2 mb-2 mt-2"><span/><code>$ cpuid <span class="p">|</span> grep -i cache
</code></pre></div>
<p class=" font-serif my-1"><img alt="" src="./assets/cache.png"/></p>
</div> </section>
<section> <div>
<h2 class=" text-xl mt-2 pb-2 font-sans">TLB 相关问题</h2>
<p class=" font-serif my-1">TLB 会不够用吗？</p>
<ul class=" list-disc font-serif">
<li class=" ml-8">prefetch</li>
<li class=" ml-8">L1 hidden latency </li>
</ul>
<p class=" font-serif my-1">process switch 带来的问题</p>
<ul class=" list-disc font-serif">
<li class=" ml-8">flush TLB</li>
<li class=" ml-8"><a href="https://stackoverflow.com/questions/52813239/how-many-bits-there-are-in-a-tlb-asid-tag-for-intel-processors-and-how-to-handl">tagged TLB(ASID)</a></li>
</ul>
<p class=" font-serif my-1">还有其他问题: cache management, cache coherence .etc</p>
</div> </section>
<section> <div>
<h2 class=" text-xl mt-2 pb-2 font-sans">虚拟内存的用处</h2>
<ul class=" list-disc font-serif">
<li class=" ml-8">物理内存多时: prefetch(投机)</li>
<li class=" ml-8">物理内存少时: swap</li>
<li class=" ml-8">内存保护 (P.18)</li>
<li class=" ml-8">链接和加载更容易 </li>
<li class=" ml-8">按需分配(COW)</li>
<li class=" ml-8">实现 <a href="https://eli.thegreenplace.net/2011/01/27/how-debuggers-work-part-2-breakpoints">watch point</a></li>
</ul>
<div class="codehilite"><pre class=" bg-gray-100 overflow-x-auto rounded p-2 mb-2 mt-2"><span/><code>$ gcc mmap-alloc.c <span class="o">&&</span> ./a.out
</code></pre></div>
</div> </section>
<section> <div>
<h2 class=" text-xl mt-2 pb-2 font-sans">Memory Copy</h2>
<p class=" font-serif my-1">内核与空间交互数据需要进行数据的拷贝
<img alt="" src="./assets/memory_copy.png"/></p>
</div> </section>
<section> <div>
<h2 class=" text-xl mt-2 pb-2 font-sans">Memory-Mapping</h2>
<p class=" font-serif my-1">没有中间商赚差价</p>
<ul class=" list-disc font-serif">
<li class=" ml-8">映射文件</li>
<li class=" ml-8">映射设备<ul class=" list-disc font-serif">
<li class=" ml-8"><a href="https://docs.kernel.org/networking/packet_mmap.html">Packet MMAP</a></li>
</ul>
</li>
<li class=" ml-8">进程间共享内存</li>
</ul>
</div> </section>
</section>
<section>
<div>
<h2 class=" text-xl mt-2 pb-2 font-sans">内存分配</h2>
<ul class=" list-disc font-serif">
<li class=" ml-8">链表</li>
<li class=" ml-8">fixed page pool</li>
<li class=" ml-8">伙伴系统</li>
</ul>
</div>
</section>
<section>
<div>
<h2 class=" text-xl mt-2 pb-2 font-sans">Garbage Collect</h2>
<ul class=" list-disc font-serif">
<li class=" ml-8">reference conuting<ul class=" list-disc font-serif">
<li class=" ml-8">COW</li>
</ul>
</li>
<li class=" ml-8">mark sweep</li>
</ul>
<p class=" font-serif my-1">参考书籍</p>
<ul class=" list-disc font-serif">
<li class=" ml-8"><a href="https://book.douban.com/subject/26821357/">垃圾回收的算法与实现</a></li>
</ul>
</div>
</section>
</div>
</div>
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