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Date:   Wed, 12 May 2021 12:50:22 +0300
From:   Ilias Apalodimas <ilias.apalodimas@linaro.org>
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     Matteo Croce <mcroce@linux.microsoft.com>, netdev@vger.kernel.org,
        linux-mm@kvack.org, Ayush Sawal <ayush.sawal@chelsio.com>,
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        Jesper Dangaard Brouer <hawk@kernel.org>,
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        Boris Pismenny <borisp@nvidia.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>, Yu Zhao <yuzhao@google.com>,
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        Andrew Lunn <andrew@lunn.ch>, Paolo Abeni <pabeni@redhat.com>,
        Sven Auhagen <sven.auhagen@voleatech.de>
Subject: Re: [PATCH net-next v4 2/4] page_pool: Allow drivers to hint on SKB
 recycling
Message-ID: <YJuk3o6CezbVrT+P@apalos.home>
References: <20210511133118.15012-1-mcroce@linux.microsoft.com>
 <20210511133118.15012-3-mcroce@linux.microsoft.com>
 <fa93976a-3460-0f7f-7af4-e78bfe55900a@gmail.com>
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[...]
> > Since we added an extra argument on __skb_frag_unref() to handle
> > recycling, update the current users of the function with that.
> 
> This part could be done with a preliminary patch, only adding this
> extra boolean, this would keep the 'complex' patch smaller.

Sure 

[...]
> >  #include <linux/uaccess.h>
> >  #include <trace/events/skb.h>
> > @@ -645,6 +648,11 @@ static void skb_free_head(struct sk_buff *skb)
> >  {
> >  	unsigned char *head = skb->head;
> >  
> > +#if IS_BUILTIN(CONFIG_PAGE_POOL)
> 
> Why IS_BUILTIN() ? 

No reason, we'll replace it with an ifdef

> 
> PAGE_POOL is either y or n
> 
> IS_ENABLED() would look better, since we use IS_BUILTIN() for the cases where a module might be used.
> 
> Or simply #ifdef CONFIG_PAGE_POOL
> 
> > +	if (skb->pp_recycle && page_pool_return_skb_page(head))
> 
> This probably should be attempted only in the (skb->head_frag) case ?

I think the extra check makes sense.

> 
> Also this patch misses pskb_expand_head()

I am not sure I am following. Misses what? pskb_expand_head() will either
call skb_release_data() or skb_free_head(), which would either recycle or
unmap the buffer for us (depending on the page refcnt)

[...]

Thanks
/Ilias