netdev - Re: [PATCH net-next] net: more accurate skb truesize

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Message-Id: <20111013.160552.102035093902771886.davem@davemloft.net>
Date:	Thu, 13 Oct 2011 16:05:52 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	bhutchings@...arflare.com, netdev@...r.kernel.org,
	ak@...ux.intel.com
Subject: Re: [PATCH net-next] net: more accurate skb truesize

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 13 Oct 2011 19:28:54 +0200

> [PATCH V2 net-next] net: more accurate skb truesize
> 
> skb truesize currently accounts for sk_buff struct and part of skb head.
> kmalloc() roundings are also ignored.
> 
> Considering that skb_shared_info is larger than sk_buff, its time to
> take it into account for better memory accounting.
> 
> This patch introduces SKB_TRUESIZE(X) macro to centralize various
> assumptions into a single place.
> 
> At skb alloc phase, we put skb_shared_info struct at the exact end of
> skb head, to allow a better use of memory (lowering number of
> reallocations), since kmalloc() gives us power-of-two memory blocks.
> 
> Unless SLUB/SLUB debug is active, both skb->head and skb_shared_info are
> aligned to cache lines, as before.
> 
> Note: This patch might trigger performance regressions because of
> misconfigured protocol stacks, hitting per socket or global memory
> limits that were previously not reached. But its a necessary step for a
> more accurate memory accounting.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

Applied.
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