netdev - Re: [PATCH 04/16] mm: allow PF_MEMALLOC from softirq context

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Message-ID: <20120626165513.GD6509@breakpoint.cc>
Date:	Tue, 26 Jun 2012 18:55:13 +0200
From:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>, Neil Brown <neilb@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Christie <michaelc@...wisc.edu>,
	Eric B Munson <emunson@...bm.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH 04/16] mm: allow PF_MEMALLOC from softirq context

On Fri, Jun 22, 2012 at 03:30:31PM +0100, Mel Gorman wrote:
> This is needed to allow network softirq packet processing to make
> use of PF_MEMALLOC.

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b6c0727..5c6d9c6 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2265,7 +2265,11 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
>  	if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) {
>  		if (gfp_mask & __GFP_MEMALLOC)
>  			alloc_flags |= ALLOC_NO_WATERMARKS;
> -		else if (likely(!(gfp_mask & __GFP_NOMEMALLOC)) && !in_interrupt())
> +		else if (in_serving_softirq() && (current->flags & PF_MEMALLOC))
> +			alloc_flags |= ALLOC_NO_WATERMARKS;
> +		else if (!in_interrupt() &&
> +				((current->flags & PF_MEMALLOC) ||
> +				 unlikely(test_thread_flag(TIF_MEMDIE))))
>  			alloc_flags |= ALLOC_NO_WATERMARKS;
>  	}

You allocate in RX path with __GFP_MEMALLOC and your sk->sk_allocation has
also __GFP_MEMALLOC set. That means you should get ALLOC_NO_WATERMARKS in
alloc_flags. Is this to done to avoid GFP annotations in skb_share_check() and
friends on your __netif_receive_skb() path?

Sebastian
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