Re: [RFC 0/3] bootmem rewrite
From: Johannes Weiner
Date: Wed May 21 2008 - 20:34:25 EST
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:
> On Wed, 21 May 2008 03:37:35 +0200
> Johannes Weiner <hannes@xxxxxxxxxxxx> wrote:
>> This is a complete overhaul of the bootmem allocator while preserving
>> its original functionality, excluding bugs.
> Where angels fear to tread.
Anyone who has seen this code realizes that this kind of advertisment is
essential to get people looking at patches for it ;)
>> free_bootmem and reserve_bootmem become a bit stricter than they are
>> right now, callsites have to make sure that the PFN range is
>> contiguous but it might go across node boundaries.
>> alloc_bootmem satisfying the allocation goal is more likely as the
>> routines will try to allocate on the node holding the goal first
>> before falling back as opposed to the original behaviour that
>> satisfies the goal only if it is on the first node.
>> All in all, I think the code has become simpler and cleaner. All
>> public interfaces have been documented, too.
>> The first patch moves the bootmem node descriptor definitions into
>> bootmem.c where they belong.
>> The second patch is the new allocator itself.
>> The third patch converts all users of ->node_boot_start to
>> ->node_min_pfn as this is what they really use. It then removes the
>> unused ->node_boot_start.
>> Compile and runtime tested on X86_32, therefor RFC only.
>> arch/alpha/mm/numa.c | 8 +-
>> arch/arm/mm/discontig.c | 34 +-
>> arch/arm/plat-omap/fb.c | 4 +-
>> arch/avr32/mm/init.c | 3 +-
>> arch/ia64/mm/discontig.c | 30 +-
>> arch/m32r/mm/discontig.c | 4 +-
>> arch/m32r/mm/init.c | 4 +-
>> arch/m68k/mm/init.c | 4 +-
>> arch/mips/sgi-ip27/ip27-memory.c | 3 +-
>> arch/mn10300/mm/init.c | 6 +-
>> arch/parisc/mm/init.c | 3 +-
>> arch/powerpc/mm/numa.c | 3 +-
>> arch/sh/mm/init.c | 2 +-
>> arch/sh/mm/numa.c | 5 +-
>> arch/sparc64/mm/init.c | 3 +-
>> arch/x86/mm/discontig_32.c | 3 +-
>> arch/x86/mm/numa_64.c | 6 +-
>> include/linux/bootmem.h | 115 ++---
>> mm/bootmem.c | 914 +++++++++++++++++++-------------------
>> mm/page_alloc.c | 4 +-
> Oh gee.
Okay, seeing it again it looks a bit brutal. But it's not. The basic
principles are the same, it's not that I completely changed the
implementation. Okay, perhaps I did.
And the arch changes are trivial.
> bootmem is an area where large numbers of people have done hit-and-run
> jobs over a lot of years. Nobody owns it and I'm sure that you are now
> the world's expert. We just need to push ahead with this, I guess.
> I expect there will be problems - so many architectures which do such
> different things, and all the configuration options churning things
I expect problems too. I just can not go any further with it on the
resources I have.
> So how to move ahead with this?
> - I think I'd prefer not to drop
> because those are small, simple things which are on track for
> 2.6.27 whereas a massive rewrite may take longer to get merged, and
> may never get there at all, in which case we lost those little
I can see that.
> - It would suit my purposes to have these patches right at the tail
> of the -mm patch queue so that I can drop them easily if problems
> occur, and so that others can revert them easily when diagnosing
> - It would be nice to get some review attention from architecture
> guys, but I can understand them finding other things to do, when
> bootmem is presumably good-enough-for-now.
> - Is x86_32 the only test platform which you have available? Awkward.
Yes, unfortunately. Hardware offers via private mail, please!
> Anyway, if you can redo these patches against most-recent-mm or,
> better, against http://userweb.kernel.org/~akpm/mmotm then it would
> make things easier for me to handle. I can then at least test it all
> on my seven-odd test boxes. Please feel free to ping me if you want a
> single rolled-up patch - that's always trivial and I can do it in three
I guess I just apply the quilt series to the tree you forked off?
> Finally, if you haven't done so, I'd encourage you to stuff as many
> handy debugging printks into this code as you possibly can. Just fill
> 'er up with them. So that when people start running it and it goes
> boom, they can send you their debug output _without_ having to go
> through another handful of email-email-patch-rebuild-retest cycles. We
> can pull them all out later on.
Okay, I will make it gossip and send you a -mmotm-based version of it.
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