Messages in this thread |  | | | From | Rusty Russell <> | | Subject | Re: [PATCH 09/10] percpu: implement new dynamic percpu allocator | | Date | Tue, 24 Feb 2009 13:26:22 +1030 |
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On Friday 20 February 2009 13:31:21 Tejun Heo wrote: > > One question. Are you thinking that to be defined by every SMP arch > > long-term? > > Yeap, definitely.
Excellent. That opens some really nice stuff.
> > Because there are benefits in having &<percpuvar> == valid > > percpuptr, such as passing them around as parameters. If so, IA64 > > will want a dedicated per-cpu area for statics (tho it can probably > > just map it somehow, but it has to be 64k). > > Hmmm... Don't have much idea about ia64 and its magic 64k. Can it > somehow be used for the first chunk?
Yes, but I think that chunk must not be handed out for dynamic allocations but kept in reserve for modules.
IA64 uses a pinned TLB entry to map this cpu's 64k at __phys_per_cpu_start. See __ia64_per_cpu_var() in arch/ia64/include/asm/percpu.h. This means they can also optimize cpu_local_* and read_cpuvar (or whatever it's called now). IIUC IA64 needs this region internally, using it for percpu vars is a bonus.
> > These pseudo-constants seem like a really weird thing to do to me. > > I explained this in the reply to Andrew's comment. It's > non-really-constant-but-should-be-considered-so-by-users thing. Is it > too weird? Even if I add comment explaning it?
It's weird; I'd make them __read_mostly and be done with it.
> > rbtree might be overkill on first cut. I'm bearing in mind that Christoph L > > had a nice patch to use dynamic percpu allocation in the sl*b allocators; > > which would mean this needs to only use get_free_page. > > Hmmm... the reverse mapping can be piggy backed on vmalloc by adding a > private pointer to the vm_struct but rbtree isn't too difficult to use > so I just did it directly. Nick, what do you think about adding > private field to vm_struct and providing a reverse map function?
Naah, just walk the arrays to do the mapping. Cuts a heap of code, and we can optimize when someone complains :)
Walking arrays is cache friendly, too.
> As for the sl*b allocation thing, can you please explain in more > detail or point me to the patches / threads?
lkml from 2008-05-30:
Message-Id: <20080530040021.800522644@sgi.com>: Subject: [patch 32/41] cpu alloc: Use in slub And: Subject: [patch 33/41] cpu alloc: Remove slub fields Subject: [patch 34/41] cpu alloc: Page allocator conversion
> Thanks. :-)
Don't thank me: you're doing all the work! Rusty.
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