Messages in this thread | | | Date | Tue, 08 Apr 2008 23:55:45 -0700 | From | Mike Travis <> | Subject | Re: bootmem allocator |
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Andi Kleen wrote: > 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
Hi Andi,
I really don't care(*), but there's lot's of code that expects a certain behavior. Either all the source calls have to be modified en masse (and you well know that's difficult given the _zillion_ source trees), or you have to introduce the new API transparently. That means leaving a backdoor for old calls:
#define bootmem_alloc_low(...) \ __new_bootmem_alloc(..., FLAGS_FOR_OLD_BOOTMEM_ALLOC_LOW);
Then I think you're free to optimize away... d;-) [happy face with a baseball cap]
Cheers, Mike
(*) As long as I don't have to debug problems as a result of the change...! ;-)
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