netdev - Re: [PATCH net-next 1/3] net: allow > 0 order atomic page alloc in skb_page_frag

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Date:	Mon, 23 Dec 2013 14:53:21 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Michael Dalton <mwdalton@...gle.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jason Wang <jasowang@...hat.com>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next 1/3] net: allow > 0 order atomic page alloc in
 skb_page_frag_refill

On Mon, Dec 16, 2013 at 04:16:27PM -0800, Michael Dalton wrote:
> skb_page_frag_refill currently permits only order-0 page allocs
> unless GFP_WAIT is used. Change skb_page_frag_refill to attempt
> higher-order page allocations whether or not GFP_WAIT is used. If
> memory cannot be allocated, the allocator will fall back to
> successively smaller page allocs (down to order-0 page allocs).
> 
> This change brings skb_page_frag_refill in line with the existing
> page allocation strategy employed by netdev_alloc_frag, which attempts
> higher-order page allocations whether or not GFP_WAIT is set, falling
> back to successively lower-order page allocations on failure. Part
> of migration of virtio-net to per-receive queue page frag allocators.
> 
> Signed-off-by: Michael Dalton <mwdalton@...gle.com>

I don't get how this is related to patch 3/3 exactly.
That one seems to clamp the allocations from ewma to at most
PAGE_SIZE, so how to we get higher-order allocations here?
Could you clarify please?

> ---
>  net/core/sock.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/net/core/sock.c b/net/core/sock.c
> index ab20ed9..7383d23 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1865,9 +1865,7 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t prio)
>  		put_page(pfrag->page);
>  	}
>  
> -	/* We restrict high order allocations to users that can afford to wait */
> -	order = (prio & __GFP_WAIT) ? SKB_FRAG_PAGE_ORDER : 0;
> -
> +	order = SKB_FRAG_PAGE_ORDER;
>  	do {
>  		gfp_t gfp = prio;
>  
> -- 
> 1.8.5.1
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