linux-kernel - Re: [PATCH net-next v3 2/2] net/smc: handle -ENOMEM from smc_wr_alloc_link

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Message-ID: <cd1c6040-0a8f-45fb-91aa-2df2c5ae085a@redhat.com>
Date: Thu, 25 Sep 2025 11:40:40 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Halil Pasic <pasic@...ux.ibm.com>, Jakub Kicinski <kuba@...nel.org>,
 Simon Horman <horms@...nel.org>, "D. Wythe" <alibuda@...ux.alibaba.com>,
 Dust Li <dust.li@...ux.alibaba.com>, Sidraya Jayagond
 <sidraya@...ux.ibm.com>, Wenjia Zhang <wenjia@...ux.ibm.com>,
 Mahanta Jambigi <mjambigi@...ux.ibm.com>, Tony Lu
 <tonylu@...ux.alibaba.com>, Wen Gu <guwen@...ux.alibaba.com>,
 netdev@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
 linux-s390@...r.kernel.org
Subject: Re: [PATCH net-next v3 2/2] net/smc: handle -ENOMEM from
 smc_wr_alloc_link_mem gracefully

On 9/21/25 11:44 PM, Halil Pasic wrote:
> @@ -836,27 +838,39 @@ int smcr_link_init(struct smc_link_group *lgr, struct smc_link *lnk,
>  	rc = smc_llc_link_init(lnk);
>  	if (rc)
>  		goto out;
> -	rc = smc_wr_alloc_link_mem(lnk);
> -	if (rc)
> -		goto clear_llc_lnk;
>  	rc = smc_ib_create_protection_domain(lnk);
>  	if (rc)
> -		goto free_link_mem;
> -	rc = smc_ib_create_queue_pair(lnk);
> -	if (rc)
> -		goto dealloc_pd;
> +		goto clear_llc_lnk;
> +	do {
> +		rc = smc_ib_create_queue_pair(lnk);
> +		if (rc)
> +			goto dealloc_pd;
> +		rc = smc_wr_alloc_link_mem(lnk);
> +		if (!rc)
> +			break;
> +		else if (rc != -ENOMEM) /* give up */
> +			goto destroy_qp;
> +		/* retry with smaller ... */
> +		lnk->max_send_wr /= 2;
> +		lnk->max_recv_wr /= 2;
> +		/* ... unless droping below old SMC_WR_BUF_SIZE */
> +		if (lnk->max_send_wr < 16 || lnk->max_recv_wr < 48)
> +			goto destroy_qp;

If i.e. smc.sysctl_smcr_max_recv_wr == 2048, and
smc.sysctl_smcr_max_send_wr == 16, the above loop can give-up a little
too early - after the first failure. What about changing the termination
condition to:

	lnk->max_send_wr < 16 && lnk->max_recv_wr < 48

and use 2 as a lower bound for both lnk->max_send_wr and lnk->max_recv_wr?

Thanks,

Paolo