linux-kernel - Re: [patch 1/2] ufd v1 - unsequential O(1) fdmap core

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Date:	Mon, 4 Jun 2007 09:56:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Eric Dumazet <dada1@...mosbay.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [patch 1/2] ufd v1 - unsequential O(1) fdmap core

On Mon, 4 Jun 2007 06:05:22 -0700 (PDT) Davide Libenzi <davidel@...ilserver.org> wrote:

> On Mon, 4 Jun 2007, Andrew Morton wrote:
> 
> > a) Were IDR trees evaluated and if so, why were they rejected?
> > 
> > b) it's a bit disappointing that this new allocator is only usable for
> >    one specific application.  We have a *lot* of places in the kernel which
> >    want allocators of this type.  Many of them are open-coded and crappy. 
> >    Some use IDR trees.
> > 
> >    If we're going to go and add a complete new allocator, it would be
> >    good to position it as a library thing if poss.
> 
> Thank you for pointing me to that, Andrew. I didn't know about it (IDR 
> trees).
> It does not fit AFAICS.
> Locking should be handled extarnally (the files 
> struct),

Yeah, that's already a problem in IDR and I'm hoping sometime someone will
be inspired to redo it, move it to caller-provided locking.

> must be RCU friendly (proper barriers) since it's used in 
> lockless code,

Haven't looked at that.

> and must have flags associated to an allocation.

Don't understand that.

> And I'm 
> leaving out the O(1) part, that for something like this, is just silly not 
> to have it. This is really an array.

Having to walk down a tree in fget_light() would kinda suck.

What about my b)?
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