linux-kernel - Re: [patch 7/8] fdmap v2

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Message-ID: <Pine.LNX.4.64.0706071243090.6445@alien.or.mcafeemobile.com>
Date:	Thu, 7 Jun 2007 12:49:07 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	Kyle Moffett <mrmacman_g4@....com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2

On Thu, 7 Jun 2007, Eric Dumazet wrote:

> Davide, are you sure we want FIFO for non sequential allocations ?
> 
> This tends to use all the fmap slots, and not very cache friendly
> if an app does a lot of [open(),...,close()] things. We already got a 
> perf drop because of RCUification of file freeing (FIFO mode instead 
> of LIFO given by kmalloc()/kfree())
> 
> If the idea behind this FIFO was security (ie not easy for an app to predict 
> next glibc file handle), we/glibc might use yet another FD_SECUREMODE flag, 
> wich ORed with O_NONSEQFD would ask to fdmap_newfd() to take the tail of 
> fmap->slist, not head.

Uli, would it be OK to rely only on base randomization and use a LIFO 
instead? We have base randomization, plus LIFO does not mean strictly 
sequential like legacy allocator, just more compatc and cache friendly.



- Davide


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