linux-kernel - Re: [PATCH] fdtable: Eradicate fdarray overflow.

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Message-id: <452DD058.7000301@cosmosbay.com>
Date:	Thu, 12 Oct 2006 07:19:20 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Vadim Lobanov <vlobanov@...akeasy.net>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fdtable: Eradicate fdarray overflow.

Vadim Lobanov a écrit :
> 
> diff -Npru old/fs/file.c new/fs/file.c
> --- old/fs/file.c	2006-10-10 18:58:21.000000000 -0700
> +++ new/fs/file.c	2006-10-11 19:37:23.000000000 -0700
> @@ -164,9 +164,8 @@ static struct fdtable * alloc_fdtable(un
>  	 * the fdarray into page-sized chunks: starting at a quarter of a page,
>  	 * and growing in powers of two from there on.
>  	 */
> -	nr++;
>  	nr /= (PAGE_SIZE / 4 / sizeof(struct file *));
> -	nr = roundup_pow_of_two(nr);
> +	nr = roundup_pow_of_two(nr + 1);
>  	nr *= (PAGE_SIZE / 4 / sizeof(struct file *));
>  	if (nr > NR_OPEN)
>  		nr = NR_OPEN;

Hi Vadim

I find your PAGE_SIZE/4 minimum allocation quite unjustified.

For architectures with 64K PAGE_SIZE, we endup allocating 16K, for poor tasks 
that happen to touch a not so high (>= 64) file descriptor...

I would vote for a fixed size, like 1024

Eric
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