Re: Temporary memory allocation from interrupt context

[Jason Thorpe <thorpej%me.com@localhost>]

> On Nov 11, 2020, at 5:38 AM, Martin Husemann <martin%duskware.de@localhost> wrote:
> 
> Yes, and of course the real code has that (and works). It's just that 
> - memoryallocators(9) does not cover this case
> - kmem_intr_alloc(9) is kinda deprecated - quoting the man page:
> 
> 	These routines are for the special cases.  Normally,
> 	pool_cache(9) should be used for memory allocation from interrupt
> 	context.
> 
>   but how would I use pool_cache(9) here?

It's not "deprecated" per se.  Heck, kmem_intr_alloc() was added *after* the pool cache API was added :-).  Sounds to me like memoryallocators(9) needs to be combed through and updated.

Anyway, I think what the documentation is trying to convey is that "pool_cache is better if you are allocating and freeing fixed size objects in a hot code path".  However, you're not allocating fixed-size objects, so using pool_cache directly is not appropriate.  Using kmem_intr_alloc() is preferable to rolling your own logic here, and gets you the optimal behavior for this use case.

-- thorpej