linux-kernel - [PATCH net-next 1/3] net/smc: cap allocation order for SMC-R physically contiguous buffers

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Message-ID: <20260123082349.42663-2-alibuda@linux.alibaba.com>
Date: Fri, 23 Jan 2026 16:23:47 +0800
From: "D. Wythe" <alibuda@...ux.alibaba.com>
To: "David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dust Li <dust.li@...ux.alibaba.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Sidraya Jayagond <sidraya@...ux.ibm.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Wenjia Zhang <wenjia@...ux.ibm.com>
Cc: Mahanta Jambigi <mjambigi@...ux.ibm.com>,
	Simon Horman <horms@...nel.org>,
	Tony Lu <tonylu@...ux.alibaba.com>,
	Wen Gu <guwen@...ux.alibaba.com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-rdma@...r.kernel.org,
	linux-s390@...r.kernel.org,
	netdev@...r.kernel.org,
	oliver.yang@...ux.alibaba.com
Subject: [PATCH net-next 1/3] net/smc: cap allocation order for SMC-R physically contiguous buffers

The alloc_page() cannot satisfy requests exceeding MAX_PAGE_ORDER,
and attempting such allocations will lead to guaranteed failures
and potential kernel warnings.

For SMCR_PHYS_CONT_BUFS, the allocation order is now capped to
MAX_PAGE_ORDER, ensures the attempts to allocate the largest possible
physically contiguous chunk instead of failing with an invalid order,
which also avoid redundant "try-fail-degrade" cycles in __smc_buf_create().

For SMCR_MIXED_BUFS, If it's order exceeds MAX_PAGE_ORDER, skips the
doomed physical allocation attempt and fallback to virtual memory
immediately.

Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
Reviewed-by: Dust Li <dust.li@...ux.alibaba.com>
---
 net/smc/smc_core.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index e4eabc83719e..6219db498976 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -2324,26 +2324,30 @@ static struct smc_buf_desc *smcr_new_buf_create(struct smc_link_group *lgr,
 	if (!buf_desc)
 		return ERR_PTR(-ENOMEM);
 
+	buf_desc->order = get_order(bufsize);
+
 	switch (lgr->buf_type) {
 	case SMCR_PHYS_CONT_BUFS:
+		buf_desc->order = min(buf_desc->order, MAX_PAGE_ORDER);
+		fallthrough;
 	case SMCR_MIXED_BUFS:
-		buf_desc->order = get_order(bufsize);
-		buf_desc->pages = alloc_pages(GFP_KERNEL | __GFP_NOWARN |
-					      __GFP_NOMEMALLOC | __GFP_COMP |
-					      __GFP_NORETRY | __GFP_ZERO,
-					      buf_desc->order);
-		if (buf_desc->pages) {
-			buf_desc->cpu_addr =
-				(void *)page_address(buf_desc->pages);
-			buf_desc->len = bufsize;
-			buf_desc->is_vm = false;
-			break;
+		if (buf_desc->order <= MAX_PAGE_ORDER) {
+			buf_desc->pages = alloc_pages(GFP_KERNEL | __GFP_NOWARN |
+						      __GFP_NOMEMALLOC | __GFP_COMP |
+						      __GFP_NORETRY | __GFP_ZERO,
+						      buf_desc->order);
+			if (buf_desc->pages) {
+				buf_desc->cpu_addr =
+					(void *)page_address(buf_desc->pages);
+				buf_desc->len = bufsize;
+				buf_desc->is_vm = false;
+				break;
+			}
 		}
 		if (lgr->buf_type == SMCR_PHYS_CONT_BUFS)
 			goto out;
 		fallthrough;	// try virtually contiguous buf
 	case SMCR_VIRT_CONT_BUFS:
-		buf_desc->order = get_order(bufsize);
 		buf_desc->cpu_addr = vzalloc(PAGE_SIZE << buf_desc->order);
 		if (!buf_desc->cpu_addr)
 			goto out;
-- 
2.45.0