netdev - Re: [RFC V3] net: don't wait for order-3 page allocation

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Date:	Thu, 11 Jun 2015 17:34:19 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	shli@...com
Cc:	netdev@...r.kernel.org, Kernel-team@...com, clm@...com,
	linux-mm@...ck.org, dbavatar@...il.com, edumazet@...gle.com
Subject: Re: [RFC V3] net: don't wait for order-3 page allocation

From: Shaohua Li <shli@...com>
Date: Thu, 11 Jun 2015 16:50:48 -0700

> We saw excessive direct memory compaction triggered by skb_page_frag_refill.
> This causes performance issues and add latency. Commit 5640f7685831e0
> introduces the order-3 allocation. According to the changelog, the order-3
> allocation isn't a must-have but to improve performance. But direct memory
> compaction has high overhead. The benefit of order-3 allocation can't
> compensate the overhead of direct memory compaction.
> 
> This patch makes the order-3 page allocation atomic. If there is no memory
> pressure and memory isn't fragmented, the alloction will still success, so we
> don't sacrifice the order-3 benefit here. If the atomic allocation fails,
> direct memory compaction will not be triggered, skb_page_frag_refill will
> fallback to order-0 immediately, hence the direct memory compaction overhead is
> avoided. In the allocation failure case, kswapd is waken up and doing
> compaction, so chances are allocation could success next time.
> 
> alloc_skb_with_frags is the same.
> 
> The mellanox driver does similar thing, if this is accepted, we must fix
> the driver too.
> 
> V3: fix the same issue in alloc_skb_with_frags as pointed out by Eric
> V2: make the changelog clearer
> 
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Chris Mason <clm@...com>
> Cc: Debabrata Banerjee <dbavatar@...il.com>
> Signed-off-by: Shaohua Li <shli@...com>

Applied and queued up for -stable, thanks!
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