GFP_ATOMIC or GFP_KERNEL?

最新推荐文章于 2025-08-21 07:57:04 发布

转载最新推荐文章于 2025-08-21 07:57:04 发布 · 645 阅读

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#linux内核

本文探讨了Linux内核中GFP_ATOMIC和GFP_KERNEL标志的使用场景及其区别。GFP_ATOMIC使分配操作具备原子性，适用于中断处理程序；而GFP_KERNEL则更努力地寻找内存，但可能引起睡眠，不适用于中断上下文。文章还讨论了kmalloc和vmalloc在不同内存需求下的应用。

本文转载至：http://lists.metaprl.org/pipermail/cs134-labs/2002-October/000025.html

The short (or kinda long) answer is this:

GFP_ATOMIC means roughly "make the allocation operation atomic".  This
means that the kernel will try to find the memory using a pile of free
memory set aside for urgent allocation.  If that pile doesn't have
enough free pages, the operation will fail.  This flag is useful for
allocation within interrupt handlers.

GFP_KERNEL will try a little harder to find memory.  There's a
possibility that the call to kmalloc() will sleep while the kernel is
trying to find memory (thus making it unsuitable for interrupt
handlers).  It's much more rare for an allocation with GFP_KERNEL to
fail than with GFP_ATOMIC.

In all cases, kmalloc() should only be used allocating small amounts of
memory (a few kb).  vmalloc() is better for larger amounts.

Also note that in lab 1 and lab 2, it would have been arguably better to
use GFP_KERNEL instead of GFP_ATOMIC.  GFP_ATOMIC should be saved for
those instances in which a sleep would be totally unacceptable.

This is a fuzzy issue though...there's no absolute right or wrong
answer.