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

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Message-ID: <Pine.LNX.4.64.0706040533210.30231@alien.or.mcafeemobile.com>
Date:	Mon, 4 Jun 2007 06:05:22 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Andrew Morton <akpm@...ux-foundation.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, 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), must be RCU friendly (proper barriers) since it's used in 
lockless code, and must have flags associated to an allocation. 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.



- Davide


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