netdev - Re: [PATCH v2 net-next 3/3] tuntap: reduce the size of tun

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Date:	Tue, 25 Nov 2014 13:27:17 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	pagupta@...hat.com
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jasowang@...hat.com, dgibson@...hat.com, vfalico@...il.com,
	edumazet@...gle.com, vyasevic@...hat.com, hkchu@...gle.com,
	xemul@...allels.com, therbert@...gle.com,
	bhutchings@...arflare.com, xii@...gle.com,
	stephen@...workplumber.org, jiri@...nulli.us,
	sergei.shtylyov@...entembedded.com
Subject: Re: [PATCH v2 net-next 3/3] tuntap: reduce the size of tun_struct
 by using flex array.

From: Pankaj Gupta <pagupta@...hat.com>
Date: Tue, 25 Nov 2014 00:04:04 +0530

> This patch switches to flex array to implement the flow caches, it brings
> several advantages:
> 
> - Reduce the size of the tun_struct structure, which allows us to increase the
>   upper limit of queues in future.
> - Avoid higher order memory allocation. It will be useful when switching to
>   pure hashing in flow cache which may demand a larger size array in future.
> 
> After this patch, the size of tun_struct on x86_64 reduced from 8512 to
> 328
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Pankaj Gupta <pagupta@...hat.com>
> Reviewed-by: David Gibson <dgibson@...hat.com>

I see no reason to use flex arrays for this, you are preallocaing the
memory so if anything flex array is adding an unnecessary level of
redirection for every access in return for no real gains.

Just allocate the thing normally using kzalloc() or whatever.
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