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To: Miklos Szeredi <miklos@szeredi.hu>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
       jens.axboe@oracle.com, torvalds@linux-foundation.org,
       akpm@linux-foundation.org
Subject: Re: [patch] pipe: add support for shrinking and growing pipes
From: Andi Kleen <andi@firstfloor.org>
References: <E1OEmP5-0006GU-KC@pomaz-ex.szeredi.hu>
Date: Thu, 20 May 2010 14:52:15 +0200
In-Reply-To: <E1OEmP5-0006GU-KC@pomaz-ex.szeredi.hu> (Miklos Szeredi's message of "Wed\, 19 May 2010 18\:45\:55 +0200")
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Miklos Szeredi <miklos@szeredi.hu> writes:
> +
> +	/*
> +	 * We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
> +	 * expect a lot of shrink+grow operations, just free and allocate
> +	 * again like we would do for growing. If the pipe currently
> +	 * contains more buffers than arg, then return busy.
> +	 */
> +	if (arg < pipe->nrbufs)
> +		return -EBUSY;
> +
> +	bufs = kcalloc(arg, sizeof(struct pipe_buffer), GFP_KERNEL);

While this is conceptually like socket buffers, socket buffers
have sophisticated mechanisms to throttle their memory use
under low memory conditions. That's not there here?

It means every user could pin a lot of memory.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.