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SubjectRe: bootmem allocator
On Tue, Apr 08, 2008 at 11:00:28PM -0700, Mike Travis wrote:
> Ingo Molnar wrote:
> > * Andi Kleen <andi@firstfloor.org> wrote:
> >
> >>> hm, bootmem allocator is supposed to clear memory. We have a couple
> >>> of places that rely on that.
> >> I was actually considering to change that for the GB pages hugetlbfs
> >> patchkit, because memset for 1G is a little slow and not needed (will
> >> be cleared later anyways) and it might be a problem for very large
> >> systems with a lot of such pages at boot.
> >
> > changing the default behavior of bootmem alloc to be non-clearing is a
> > really bad idea that will only cause unrobustness. The proper approach
> > is to add an _opt-in_ API that does not clear memory
> > (bootmem_alloc_dontclear() or whatever), available to callers that know
> > it for sure that they dont need the clearing.
>
> Yes, changing the default of bootmem_alloc is a bad idea. I just changed
> a bunch of static arrays to bootmem alloc's and it was pointed out early
> that not only does bootmem_alloc clear memory, but also panics if it's not
> available.

There are more and more bootmem calls that don't want the panic actually.
That is why _nopanic was invented (and gets more and more variants)
At some point the default could be even switched.

I think the right way would be to survey the callers (there are not
that many) and then come up with a sane single API that caters to the
majority of them by default and passes flags for the special cases.

-Andi


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