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

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Date:	Mon, 4 Jun 2007 10:57:31 -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:

> > 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.

It needs to be able to store flags (like close-on-exec, and maybe more) 
together with a file*.

> > 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)?

Right now, I'm working on a patch that uses fdmap even for legacy 
(sequential) fd allocations. With a cleaner interface, w/out having code 
all around the kernel that access fdtable members directly. This should 
cut some code WRT using two different allocators (code in fs/file.c will 
almost zip-away), and maybe it'll look even better and have some new 
comments too ;)
It can be, in theory, completely abstracted and moved into lib/. I'll look 
into it once I completed the first cleanup, assuming the whole thing won't 
look worse than before :)

- Davide

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