netdev - Re: [PATCH] net: fix sk_page_frag() recursion from memory reclaim

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Message-ID: <20191019211856.GR18794@devbig004.ftw2.facebook.com>
Date:   Sat, 19 Oct 2019 14:18:56 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        kernel-team@...com, linux-kernel@...r.kernel.org,
        Josef Bacik <josef@...icpanda.com>
Subject: Re: [PATCH] net: fix sk_page_frag() recursion from memory reclaim

Hello,

On Sat, Oct 19, 2019 at 11:15:28AM -0700, Eric Dumazet wrote:
> It seems compiler generates better code with :
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index ab905c4b1f0efd42ebdcae333b3f0a2c7c1b2248..56de6ac99f0952bd0bc003353c094ce3a5a852f4 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2238,7 +2238,8 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp,
>   */
>  static inline struct page_frag *sk_page_frag(struct sock *sk)
>  {
> -       if (gfpflags_allow_blocking(sk->sk_allocation))
> +       if (likely((sk->sk_allocation & (__GFP_DIRECT_RECLAIM | __GFP_MEMALLOC)) ==
> +                   __GFP_DIRECT_RECLAIM))
>                 return &current->task_frag;
>  
>         return &sk->sk_frag;
> 
> 
> WDYT ?

Whatever works is fine by me.  gfpflags_allow_blocking() is clearer
than testing __GFP_DIRECT_RECLAIM directly tho.  Maybe a better way is
introducing a new gfpflags_ helper?

Thanks.

-- 
tejun