Re: cvs commit: src/sys/dev/disk/nata ata-all.c

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

Matthew Dillon wrote:
> :why do we have to call the ctor and dtor anyways?  why not do if (oc->cto=
> :r) oc->ctor(obj); ?  or am i missing something important there?
> :
> :cheers
> :  simon
>
>     I was operating under the assumption that the objcache would normally
>     have a ctor / dtor function, so I didn't want to add another conditional
>     to that path.  This isn't entirely true any more... or rather, only
>     the mbuf subsystem really uses the feature.
>
>     Ok, I AM a bit on the fence here.  I know that implementing M_ZERO adds
>     one conditional to the hot path, but the M_ flags (like M_NOWAIT) are
>     kinda integral to the allocation subsystem and I don't want to throw
>     one away just to save a few nanoseconds.

I agree.  M_NOWAIT is important to obey, but that's also no problem.  I think we can safely assume that all consumers of object cache functions do know what they want and simply disallow M_ZERO.  That's no big deal, because we don't have any of such consumers anyways.  The whole concept of an object cache collides with using M_ZERO.  Really, if you want to zero out data, use bzero.  IIRC, M_ZERO also just optimizes page-sized allocations with kmalloc(), even if.  Everybody who is using objects should be using them the right way, which implies not using M_ZERO.

cheers
 simon

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