linux-kernel-driver-dev/kmalloc.html at master · txrxlabs/linux-kernel-driver-dev · GitHub

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<html>
<font face="helvetica">
<title>Memory Allocation - kmalloc</title>
<body>
<p align=center><font size=+5>Memory Allocation - kmalloc</font>
<hr>
<a href="contents.html">Contents</a>
<font size=+3>
<ul>
<li>kmalloc/kfree
<ul>
<li><pre>static __always_inline void *kmalloc(size_t size, gfp_t flags);</pre>
Example:
<pre>
	struct mystruct *x;

	x = kmalloc(sizeof(*x), GFP_KERNEL);
</pre>
<li>You almost always want GFP_KERNEL for the flags argument.
<li>kmalloc may sleep.  Do not call it when you aren't able to
sleep, e.g. don't call it from within interrupt handlers.
<font size=-1>GFP_ATOMIC flag may enable
you to call kmalloc without sleeping, but if you think you need
this, you need to think really hard to be sure you really
do need it.</font>
<li>kmalloc will return you a virtual address that maps to
a single physically contiguous virtual address range
suitable for DMA (after mapping for DMA).
<li>You cannot kmalloc more than 128kbytes with a single call.
<li>You can call kfree with a NULL pointer, so there is no need to
do this, for example:
<pre>
	if (x) <font color="red">/* &lt;--- don't do this */</font>
		kfree(x);
</pre>Just do<pre>
	kfree(x);
</pre>
</ul>
</ul>
</font>
</body>
</html>