netdev - Re: [PATCH net] net: do not deplete pfmemalloc reserve

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Message-Id: <20150422.153532.90668848178533836.davem@davemloft.net>
Date:	Wed, 22 Apr 2015 15:35:32 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, edumazet@...gle.com, gthelen@...gle.com,
	rientjes@...gle.com, mgorman@...e.de
Subject: Re: [PATCH net] net: do not deplete pfmemalloc reserve

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 22 Apr 2015 07:33:36 -0700

> Also, we must refrain using high order pages from the pfmemalloc
> reserve, so __page_frag_refill() must also use __GFP_NOMEMALLOC for
> them. Under memory pressure, using order-0 pages is probably the best
> strategy.
 ...
> @@ -348,7 +352,8 @@ static struct page *__page_frag_refill(struct netdev_alloc_cache *nc,
>  	gfp_t gfp = gfp_mask;
>  
>  	if (order) {
> -		gfp_mask |= __GFP_COMP | __GFP_NOWARN | __GFP_NORETRY;
> +		gfp_mask |= __GFP_COMP | __GFP_NOWARN | __GFP_NORETRY |
> +			    __GFP_NOMEMALLOC;
>  		page = alloc_pages_node(NUMA_NO_NODE, gfp_mask, order);

Hmmm, skbuff.h says:

 * @gfp_mask: allocation priority. Set __GFP_NOMEMALLOC if not for network Rx

But that's exactly what this __page_frag_refill() code is primarily
being used for, network RX, right?

If we believe the comment, you should not be adding the
__GFP_NOMEMALLOC flag here.
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