linux-kernel - Re: [PATCH net-next v4] net: mana: Use page pool fragments for RX buffers instead of full pages to improve memory efficiency.

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Message-ID: <20250814011132.GA30001@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Wed, 13 Aug 2025 18:11:32 -0700
From: Dipayaan Roy <dipayanroy@...ux.microsoft.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: horms@...nel.org, kys@...rosoft.com, haiyangz@...rosoft.com,
	wei.liu@...nel.org, decui@...rosoft.com, andrew+netdev@...n.ch,
	davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
	longli@...rosoft.com, kotaranov@...rosoft.com, ast@...nel.org,
	daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
	sdf@...ichev.me, lorenzo@...nel.org, michal.kubiak@...el.com,
	ernis@...ux.microsoft.com, shradhagupta@...ux.microsoft.com,
	shirazsaleem@...rosoft.com, rosenp@...il.com,
	netdev@...r.kernel.org, linux-hyperv@...r.kernel.org,
	linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, dipayanroy@...rosoft.com
Subject: Re: [PATCH net-next v4] net: mana: Use page pool fragments for RX
 buffers instead of full pages to improve memory efficiency.

Hi Jakub,

Thank you for the review comments,

On Wed, Aug 13, 2025 at 04:48:47PM -0700, Jakub Kicinski wrote:
> On Mon, 11 Aug 2025 15:29:19 -0700 Dipayaan Roy wrote:
> > -	if (apc->port_is_up)
> > +	if (apc->port_is_up) {
> > +		/* Re-create rxq's after xdp prog was loaded or unloaded.
> > +		 * Ex: re create rxq's to switch from full pages to smaller
> > +		 * size page fragments when xdp prog is unloaded and
> > +		 * vice-versa.
> > +		 */
> > +
> > +		/* Pre-allocate buffers to prevent failure in mana_attach */
> > +		err = mana_pre_alloc_rxbufs(apc, ndev->mtu, apc->num_queues);
> > +		if (err) {
> > +			NL_SET_ERR_MSG_MOD
> > +			    (extack,
> > +			    "XDP: Insufficient memory for tx/rx re-config");
> 
> This weird line breaking is not necessary, checkpatch understands that
> string can go over line limit:
> 
> 			NL_SET_ERR_MSG_MOD(extack,
> 					   "XDP: Insufficient memory for tx/rx re-config");
> 
Ok, I willl rectify this in v5.

> > +			return err;
> 
> I think you already replaced the bpf program at this point? 
> So the allocation should happen earlier. On failure changes
> to the driver state should be undone.
The bpf prog gets completely replaced in mana_chn_setxdp,
I suggest these changes below to address your point on alloc failure
and will work on a v5:

diff --git a/drivers/net/ethernet/microsoft/mana/mana_bpf.c
b/drivers/net/ethernet/microsoft/mana/mana_bpf.c
index e616f4239294..0000c1dd7aa2 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_bpf.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_bpf.c
@@ -196,9 +196,6 @@ static int mana_xdp_set(struct net_device *ndev,
struct bpf_prog *prog,
         */
        apc->bpf_prog = prog;
 
-       if (old_prog)
-               bpf_prog_put(old_prog);
-
        if (apc->port_is_up) {
                /* Re-create rxq's after xdp prog was loaded or
 * unloaded.
                 * Ex: re create rxq's to switch from full pages to
                 * smaller
@@ -237,6 +234,9 @@ static int mana_xdp_set(struct net_device *ndev,
struct bpf_prog *prog,
                mana_pre_dealloc_rxbufs(apc);
        }
 
+       if (old_prog)
+               bpf_prog_put(old_prog);
+
        if (prog)
                ndev->max_mtu = MANA_XDP_MTU_MAX;
        else
@@ -245,6 +245,7 @@ static int mana_xdp_set(struct net_device *ndev,
struct bpf_prog *prog,
        return 0;
 
 err_dealloc_rxbuffs:
+       apc->bpf_prog = old_prog;
        mana_pre_dealloc_rxbufs(apc);
        return err;
 }

> -- 
> pw-bot: cr

Thanks
Dipayaan Roy