[lkml]   [2009]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 09/10] percpu: implement new dynamic percpu allocator
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: <>:
Subject: [patch 32/41] cpu alloc: Use in slub
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!

 \ /
  Last update: 2009-02-24 03:59    [W:0.073 / U:0.956 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site