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copied!<p>I once wrote a kernel module processing packets on a 10Gbs link. I used <code>vmalloc</code> to allocate about 1GByte of continuous (virtual) memory to put a static size hash table into it to perform connection tracking (<a href="https://github.com/diekmann/cctrack/blob/master/code/PF_RING-4.7.1/kernel/plugins/cctrack_hash.c" rel="nofollow noreferrer">code</a>).</p> <p>If you know how much memory you need, I recommend to pre-allocate it. This has two advantages</p> <ul> <li>It is fast (no mallocing/freeing at runtime)</li> <li>You don't have to think of a strategy if <code>kmalloc(_, GFP_ATOMIC)</code> can not return you memory. This can actually happen quite often under heavy load.</li> </ul> <p>Disadvantage</p> <ul> <li>You might allocate more memory then necessary.</li> </ul> <p>So, for writing a special-purpose kernel module, please pre-allocate as much memory as you can get ;)</p> <p>If you write a kernel module for commodity hardware used by many novice users, it would be nice to allocate memory on demand (and waste less memory).</p> <hr> <p>Where do you allocate memory? <code>GFP_ATOMIC</code> can only return a very small amount of memory and should only be used if your memory allocation cannot sleep. You can use <code>GFP_KERNEL</code> when it is safe to sleep, e.g., not in interrupt context. See <a href="https://stackoverflow.com/questions/116343/what-is-the-difference-between-vmalloc-and-kmalloc">this question</a> for more. It is safe to use <code>vmalloc</code> during module initialization to pre-allocate all you memory.</p>

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