linux-kernel - Re: [PATCH net-next v4 2/4] page_pool: Allow drivers to hint on SKB recycling

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Date:   Wed, 12 May 2021 12:50:22 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Matteo Croce <mcroce@...ux.microsoft.com>, netdev@...r.kernel.org,
        linux-mm@...ck.org, Ayush Sawal <ayush.sawal@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
        Rohit Maheshwari <rohitm@...lsio.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        Mirko Lindner <mlindner@...vell.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Tariq Toukan <tariqt@...dia.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Boris Pismenny <borisp@...dia.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, Yu Zhao <yuzhao@...gle.com>,
        Will Deacon <will@...nel.org>,
        Michel Lespinasse <walken@...gle.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Roman Gushchin <guro@...com>, Hugh Dickins <hughd@...gle.com>,
        Peter Xu <peterx@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexander Lobakin <alobakin@...me>,
        Cong Wang <cong.wang@...edance.com>, wenxu <wenxu@...oud.cn>,
        Kevin Hao <haokexin@...il.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Marco Elver <elver@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Guillaume Nault <gnault@...hat.com>,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        bpf@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Eric Dumazet <edumazet@...gle.com>,
        David Ahern <dsahern@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Saeed Mahameed <saeedm@...dia.com>,
        Andrew Lunn <andrew@...n.ch>, Paolo Abeni <pabeni@...hat.com>,
        Sven Auhagen <sven.auhagen@...eatech.de>
Subject: Re: [PATCH net-next v4 2/4] page_pool: Allow drivers to hint on SKB
 recycling

[...]
> > 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