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

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Date:	Wed, 26 Nov 2014 02:40:14 -0500 (EST)
From:	Pankaj Gupta <pagupta@...hat.com>
To:	David Miller <davem@...emloft.net>
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 <sergei.shtylyov@...entembedded.com>,
	"Michael S. Tsirkin" <mst@...hat.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.

I agree. Will do the changes and submit v3.
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