linux-kernel - Re: [GIT PULL v2] Early SLAB fixes for 2.6.31

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Date:	Tue, 16 Jun 2009 15:18:06 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, cl@...ux-foundation.org,
	kamezawa.hiroyu@...fujitsu.com, lizf@...fujitsu.com, mingo@...e.hu,
	yinghai@...nel.org
Subject: Re: [GIT PULL v2] Early SLAB fixes for 2.6.31

On Tue, 2009-06-16 at 06:46 +0200, Nick Piggin wrote:
> On Tue, Jun 16, 2009 at 07:31:38AM +1000, Benjamin Herrenschmidt wrote:
> > On Mon, 2009-06-15 at 13:23 +0200, Nick Piggin wrote:
> > > > I think the main problem isn't necessarily init code per se, but the
> > > > pile of -common- code that can be called both at init time and
> > > later.
> > > 
> > > Just seems bogus argument. Everwhere else that does this (ie.
> > > allocations that are called from multiple allocation contexts)
> > > passes correct gfp flags down.
> > 
> > So you say we should create new variants of all these APIs that take gfp
> > flags as arguments just because they might be called early during boot :
> 
> No, just create the ones that actually are called in early boot.

About all of the ones below and more :-) It all depends what you define
by "early" though :-)

> >  - All the vmalloc interfaces (__get_vm_area() and it's 5 or 6 variants)
> >  - Allocation of PCI host bridges data structures in the powerpc code
> >  - Allocation of interrupt controller domains in the powerpc code
> >  - Page table allocations (oops ... can't change that arch specific,
> > would have to be a generic change)
> 
> No it would not. If an arch (eg s390) does this in early boot, then
> it can create its own allocation function which takes a gfp mask, and
> define the generic one to just pass it a GFP_KERNEL. generic code does
> not call this in early boot of course.

Right, which means that ioremap needs a special code path early boot
since it uses this etc...

We are basically adding special-cases in a whole lot of places, which
could -ALL- be removed just by having the allocator do the "right
thing" :-)

> >  - ioremap (which call both __get_vm_area() and page table allocs)
> >  - ...
> > 
> > Are you just insane ? :-)
> 
> I think so, but that's besides the point ;)

Allright, I concede that :-)

Cheers,
Ben.


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