Re: separating out memory checks from INVARIANTS

On Sat, 15 Mar 2008, Kip Macy wrote:

On Sat, Mar 15, 2008 at 10:54 PM, Jeff Roberson
<jroberson@xxxxxxxxxxxxxx> wrote:

On Sat, 15 Mar 2008, Kip Macy wrote:

> I find that the serialization of memory allocation frequently hides
> race conditions. I would like to, at the very least, add an option to
> disable the memory checks if not make the memory checks a completely
> separate option. My knee jerk reaction to avoiding bikesheds is to
> simply add it to my own tree and forget about it. However, this has
> come up often enough that I feel that it warrants consideration.
>
>
> Thoughts?

One other option that I have frequently considered is to convert UMA from
using an array of bytes to using bitfields to represent the free space in
a slab. Then you could use atomics to update the required information.
It'd be a bit of work. Maybe a good SoC? :)


Would it make it possible to do memory allocation without holding a
lock in the M_NOWAIT case?

Yes, when I originally wrote the code it didn't require a lock because I relied on byte writes being atomic. However, we had platforms for which that wasn't true. (alpha). It may be that it's safe not to lock even now on x86/amd64. I don't know the specifics of the memory architectures on powerpc, arm, mips, etc. though.

Jeff


-Kip

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