[PATCH net-next v3 2/2] net/smc: handle -ENOMEM from smc_wr_alloc_link_mem gracefully

Halil Pasic
2025-09-21T21:45:04Z

Currently if a -ENOMEM from smc_wr_alloc_link_mem() is handled by
giving up and going the way of a TCP fallback. This was reasonable
before the sizes of the allocations there were compile time constants
and reasonably small. But now those are actually configurable.

So instead of giving up, keep retrying with half of the requested
size unless we dip below the old static sizes -- then give up!

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
Reviewed-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
---
Documentation/networking/smc-sysctl.rst | 8 ++++--
net/smc/smc_core.c | 34 +++++++++++++++++--------
net/smc/smc_core.h | 2 ++
net/smc/smc_wr.c | 28 ++++++++++----------
4 files changed, 46 insertions(+), 26 deletions(-)

diff --git a/Documentation/networking/smc-sysctl.rst b/Documentation/networking/smc-sysctl.rst
index c94d750c7c84..c8dbe7ac8bdf 100644
--- a/Documentation/networking/smc-sysctl.rst
+++ b/Documentation/networking/smc-sysctl.rst
@@ -85,7 +85,9 @@ smcr_max_send_wr - INTEGER

Please be aware that all the buffers need to be allocated as a physically
continuous array in which each element is a single buffer and has the size
- of SMC_WR_BUF_SIZE (48) bytes. If the allocation fails we give up much
+ of SMC_WR_BUF_SIZE (48) bytes. If the allocation fails, we keep retrying
+ with half of the buffer count until it is ether successful or (unlikely)
+ we dip below the old hard coded value which is 16 where we give up much
like before having this control.

Default: 16
@@ -103,7 +105,9 @@ smcr_max_recv_wr - INTEGER

Please be aware that all the buffers need to be allocated as a physically
continuous array in which each element is a single buffer and has the size
- of SMC_WR_BUF_SIZE (48) bytes. If the allocation fails we give up much
+ of SMC_WR_BUF_SIZE (48) bytes. If the allocation fails, we keep retrying
+ with half of the buffer count until it is ether successful or (unlikely)
+ we dip below the old hard coded value which is 16 where we give up much
like before having this control.

Default: 48
diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index 2a559a98541c..f8131b4dfcd6 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -810,6 +810,8 @@ int smcr_link_init(struct smc_link_group *lgr, struct smc_link *lnk,
lnk->clearing = 0;
lnk->path_mtu = lnk->smcibdev->pattr[lnk->ibport - 1].active_mtu;
lnk->link_id = smcr_next_link_id(lgr);
+ lnk->max_send_wr = lgr->max_send_wr;
+ lnk->max_recv_wr = lgr->max_recv_wr;
lnk->lgr = lgr;
smc_lgr_hold(lgr); /* lgr_put in smcr_link_clear() */
lnk->link_idx = link_idx;
@@ -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;
+ smc_ib_destroy_queue_pair(lnk);
+ } while (1);
+
rc = smc_wr_create_link(lnk);
if (rc)
- goto destroy_qp;
+ goto free_link_mem;
lnk->state = SMC_LNK_ACTIVATING;
return 0;

+free_link_mem:
+ smc_wr_free_link_mem(lnk);
destroy_qp:
smc_ib_destroy_queue_pair(lnk);
dealloc_pd:
smc_ib_dealloc_protection_domain(lnk);
-free_link_mem:
- smc_wr_free_link_mem(lnk);
clear_llc_lnk:
smc_llc_link_clear(lnk, false);
out:
diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h
index ab2d15929cb2..b9addf633d8a 100644
--- a/net/smc/smc_core.h
+++ b/net/smc/smc_core.h
@@ -174,6 +174,8 @@ struct smc_link {
struct completion llc_testlink_resp; /* wait for rx of testlink */
int llc_testlink_time; /* testlink interval */
atomic_t conn_cnt; /* connections on this link */
+ u16 max_send_wr;
+ u16 max_recv_wr;
};

/* For now we just allow one parallel link per link group. The SMC protocol
diff --git a/net/smc/smc_wr.c b/net/smc/smc_wr.c
index f5b2772414fd..6b14711f0c93 100644
--- a/net/smc/smc_wr.c
+++ b/net/smc/smc_wr.c
@@ -548,9 +548,9 @@ void smc_wr_remember_qp_attr(struct smc_link *lnk)
IB_QP_DEST_QPN,
&init_attr);

- lnk->wr_tx_cnt = min_t(size_t, lnk->lgr->max_send_wr,
+ lnk->wr_tx_cnt = min_t(size_t, lnk->max_send_wr,
lnk->qp_attr.cap.max_send_wr);
- lnk->wr_rx_cnt = min_t(size_t, lnk->lgr->max_recv_wr,
+ lnk->wr_rx_cnt = min_t(size_t, lnk->max_recv_wr,
lnk->qp_attr.cap.max_recv_wr);
}

@@ -742,51 +742,51 @@ int smc_wr_alloc_lgr_mem(struct smc_link_group *lgr)
int smc_wr_alloc_link_mem(struct smc_link *link)
{
/* allocate link related memory */
- link->wr_tx_bufs = kcalloc(link->lgr->max_send_wr,
+ link->wr_tx_bufs = kcalloc(link->max_send_wr,
SMC_WR_BUF_SIZE, GFP_KERNEL);
if (!link->wr_tx_bufs)
goto no_mem;
- link->wr_rx_bufs = kcalloc(link->lgr->max_recv_wr, link->wr_rx_buflen,
+ link->wr_rx_bufs = kcalloc(link->max_recv_wr, link->wr_rx_buflen,
GFP_KERNEL);
if (!link->wr_rx_bufs)
goto no_mem_wr_tx_bufs;
- link->wr_tx_ibs = kcalloc(link->lgr->max_send_wr,
+ link->wr_tx_ibs = kcalloc(link->max_send_wr,
sizeof(link->wr_tx_ibs[0]), GFP_KERNEL);
if (!link->wr_tx_ibs)
goto no_mem_wr_rx_bufs;
- link->wr_rx_ibs = kcalloc(link->lgr->max_recv_wr,
+ link->wr_rx_ibs = kcalloc(link->max_recv_wr,
sizeof(link->wr_rx_ibs[0]),
GFP_KERNEL);
if (!link->wr_rx_ibs)
goto no_mem_wr_tx_ibs;
- link->wr_tx_rdmas = kcalloc(link->lgr->max_send_wr,
+ link->wr_tx_rdmas = kcalloc(link->max_send_wr,
sizeof(link->wr_tx_rdmas[0]),
GFP_KERNEL);
if (!link->wr_tx_rdmas)
goto no_mem_wr_rx_ibs;
- link->wr_tx_rdma_sges = kcalloc(link->lgr->max_send_wr,
+ link->wr_tx_rdma_sges = kcalloc(link->max_send_wr,
sizeof(link->wr_tx_rdma_sges[0]),
GFP_KERNEL);
if (!link->wr_tx_rdma_sges)
goto no_mem_wr_tx_rdmas;
- link->wr_tx_sges = kcalloc(link->lgr->max_send_wr, sizeof(link->wr_tx_sges[0]),
+ link->wr_tx_sges = kcalloc(link->max_send_wr, sizeof(link->wr_tx_sges[0]),
GFP_KERNEL);
if (!link->wr_tx_sges)
goto no_mem_wr_tx_rdma_sges;
- link->wr_rx_sges = kcalloc(link->lgr->max_recv_wr,
+ link->wr_rx_sges = kcalloc(link->max_recv_wr,
sizeof(link->wr_rx_sges[0]) * link->wr_rx_sge_cnt,
GFP_KERNEL);
if (!link->wr_rx_sges)
goto no_mem_wr_tx_sges;
- link->wr_tx_mask = bitmap_zalloc(link->lgr->max_send_wr, GFP_KERNEL);
+ link->wr_tx_mask = bitmap_zalloc(link->max_send_wr, GFP_KERNEL);
if (!link->wr_tx_mask)
goto no_mem_wr_rx_sges;
- link->wr_tx_pends = kcalloc(link->lgr->max_send_wr,
+ link->wr_tx_pends = kcalloc(link->max_send_wr,
sizeof(link->wr_tx_pends[0]),
GFP_KERNEL);
if (!link->wr_tx_pends)
goto no_mem_wr_tx_mask;
- link->wr_tx_compl = kcalloc(link->lgr->max_send_wr,
+ link->wr_tx_compl = kcalloc(link->max_send_wr,
sizeof(link->wr_tx_compl[0]),
GFP_KERNEL);
if (!link->wr_tx_compl)
@@ -907,7 +907,7 @@ int smc_wr_create_link(struct smc_link *lnk)
goto dma_unmap;
}
smc_wr_init_sge(lnk);
- bitmap_zero(lnk->wr_tx_mask, lnk->lgr->max_send_wr);
+ bitmap_zero(lnk->wr_tx_mask, lnk->max_send_wr);
init_waitqueue_head(&lnk->wr_tx_wait);
rc = percpu_ref_init(&lnk->wr_tx_refs, smcr_wr_tx_refs_free, 0, GFP_KERNEL);
if (rc)
--
2.48.1