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| <section id="memory-in-skiboot"> |
| <h1>Memory in skiboot<a class="headerlink" href="#memory-in-skiboot" title="Link to this heading">¶</a></h1> |
| <p>There are regions of memory we statically allocate for firmware as well as |
| a HEAP region for boot and runtime allocations.</p> |
| <p>A design principle of skiboot is to attempt not to allocate memory at runtime, |
| or at least keep it to a minimum, and not do so in any critical code path |
| for the system to remain running.</p> |
| <p>At no point during runtime should a skiboot memory allocation failure cause |
| the system to stop functioning.</p> |
| <section id="heap"> |
| <h2>HEAP<a class="headerlink" href="#heap" title="Link to this heading">¶</a></h2> |
| <p>Dynamic memory allocations go in a single heap. This is identified as |
| Region ibm,firmware-heap and appears as a reserved section in the device tree.</p> |
| <p>Originally, it was 12582912 bytes in size (declared in mem_map.h). |
| Now, it is 13631488 bytes after being bumped as part of the GCOV work.</p> |
| <p>We increased heap size as on larger systems, we were getting close to using |
| all the heap once skiboot became 2MB with GCOV.</p> |
| <p>Heap usage is printed before running the payload.</p> |
| <p>For example, as of writing, on a dual socket Tuleta:</p> |
| <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">45215870591</span><span class="p">,</span><span class="mi">5</span><span class="p">]</span> <span class="n">SkiBoot</span> <span class="n">skiboot</span><span class="o">-</span><span class="mf">5.0.1</span><span class="o">-</span><span class="mi">94</span><span class="o">-</span><span class="n">gb759ce2</span> <span class="n">starting</span><span class="o">...</span> |
| <span class="p">[</span><span class="mi">3680939340</span><span class="p">,</span><span class="mi">5</span><span class="p">]</span> <span class="n">CUPD</span><span class="p">:</span> <span class="n">T</span> <span class="n">side</span> <span class="n">MI</span> <span class="n">Keyword</span> <span class="o">=</span> <span class="n">SV830_027</span> |
| <span class="p">[</span><span class="mi">3680942658</span><span class="p">,</span><span class="mi">5</span><span class="p">]</span> <span class="n">CUPD</span><span class="p">:</span> <span class="n">T</span> <span class="n">side</span> <span class="n">ML</span> <span class="n">Keyword</span> <span class="o">=</span> <span class="n">FW830</span><span class="mf">.00</span> |
| <span class="p">[</span><span class="mi">15404383291</span><span class="p">,</span><span class="mi">5</span><span class="p">]</span> <span class="n">Region</span> <span class="n">ibm</span><span class="p">,</span><span class="n">firmware</span><span class="o">-</span><span class="n">heap</span> <span class="n">free</span><span class="p">:</span> <span class="mi">5378072</span> |
| </pre></div> |
| </div> |
| <p>and on a palmetto:</p> |
| <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">24748502575</span><span class="p">,</span><span class="mi">5</span><span class="p">]</span> <span class="n">SkiBoot</span> <span class="n">skiboot</span><span class="o">-</span><span class="mf">5.0.1</span><span class="o">-</span><span class="mi">94</span><span class="o">-</span><span class="n">gb759ce2</span> <span class="n">starting</span><span class="o">...</span> |
| <span class="p">[</span><span class="mi">9870429550</span><span class="p">,</span><span class="mi">5</span><span class="p">]</span> <span class="n">Region</span> <span class="n">ibm</span><span class="p">,</span><span class="n">firmware</span><span class="o">-</span><span class="n">heap</span> <span class="n">free</span><span class="p">:</span> <span class="mi">10814856</span> |
| </pre></div> |
| </div> |
| <p>Our memory allocator is simple, a use pattern of:</p> |
| <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">A</span> <span class="o">=</span> <span class="n">malloc</span><span class="p">();</span> |
| <span class="n">B</span> <span class="o">=</span> <span class="n">malloc</span><span class="p">();</span> |
| <span class="n">free</span><span class="p">(</span><span class="n">A</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>is likely to generate fragmentation, so it should generally be avoided |
| where possible.</p> |
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| <ul> |
| <li><a class="reference internal" href="#">Memory in skiboot</a><ul> |
| <li><a class="reference internal" href="#heap">HEAP</a></li> |
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