netdev - Re: [PATCH net-next] net: ethernet: enetc: set frag flag for non-linear xdp buffers

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Message-ID: <Y49EARwosUGZfvcL@lore-desk>
Date:   Tue, 6 Dec 2022 14:30:41 +0100
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, claudiu.manoil@....com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, lorenzo.bianconi@...hat.com
Subject: Re: [PATCH net-next] net: ethernet: enetc: set frag flag for
 non-linear xdp buffers

> Hi Lorenzo,

Hi Vladimir,

> 
> On Sun, Dec 04, 2022 at 11:33:23PM +0100, Lorenzo Bianconi wrote:
> > Set missing XDP_FLAGS_HAS_FRAGS bit in enetc_add_rx_buff_to_xdp for
> > non-linear xdp buffers.
> > 
> > Fixes: d1b15102dd16 ("net: enetc: add support for XDP_DROP and XDP_PASS")
> 
> This can't be the Fixes: tag, struct xdp_buff didn't even have a "flags"
> field when that commit was introduced.

yes, my fault, I did not check dates, I assumed this commit was done after xdp
multi-buff support. We should get rid of the Fixes tag.

> 
> Also, what does this change aim to achieve? It has a Fixes: tag but it's
> aimed for net-next. Is it to enable multi-buff XDP support? But we also
> have this in place, shouldn't that be deleted too?

I think we should get rid of the chunk below as well. I am currently working on
xdp feature support in order to allow XDP_REDIRECT for S/G xdp frames.
I will post a v2.

Regards,
Lorenzo

> 
> 		case XDP_REDIRECT:
> 			/* xdp_return_frame does not support S/G in the sense
> 			 * that it leaks the fragments (__xdp_return should not
> 			 * call page_frag_free only for the initial buffer).
> 			 * Until XDP_REDIRECT gains support for S/G let's keep
> 			 * the code structure in place, but dead. We drop the
> 			 * S/G frames ourselves to avoid memory leaks which
> 			 * would otherwise leave the kernel OOM.
> 			 */
> 			if (unlikely(cleaned_cnt - orig_cleaned_cnt != 1)) {
> 				enetc_xdp_drop(rx_ring, orig_i, i);
> 				rx_ring->stats.xdp_redirect_sg++;
> 				break;
> 			}

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