linux-kernel - Re: [PATCH 2/4] Convert epoll to a bitlock

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Message-ID: <4988BD4E.8080206@cosmosbay.com>
Date:	Tue, 03 Feb 2009 22:55:26 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, oleg@...hat.com, viro@...IV.linux.org.uk,
	davidel@...ilserver.org, davem@...emloft.net, hch@....de,
	linux-api@...r.kernel.org, mpm@...enic.com,
	alan@...rguk.ukuu.org.uk
Subject: Re: [PATCH 2/4] Convert epoll to a bitlock

Andrew Morton a écrit :
> On Mon,  2 Feb 2009 11:20:09 -0700
> Jonathan Corbet <corbet@....net> wrote:
> 
>> Matt Mackall suggested converting epoll's ep_lock to a bitlock as a way of
>> saving space in struct file.  This patch makes that change.
> 
> hrm.  bit_spin_lock() makes people upset (large penguiny people).  iirc
> it doesn't have all the correct/well-understood memory/compiler
> ordering semantics which spinlocks have.  And lockdep doesn't know about
> it.
> 

In a previous attempt (2005), I suggested using a single global lock.

http://search.luky.org/linux-kernel.2005/msg50862.html

Probably an array of hashed spinlocks would be more than enough.



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