[PATCH net-next v3] net/smc: cap allocation order for SMC-R physically contiguous buffers

[PATCH net-next v3] net/smc: cap allocation order for SMC-R physically contiguous buffers

[D. Wythe]

The alloc_pages() 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, cap the allocation order to MAX_PAGE_ORDER.
This ensures the attempts to allocate the largest possible physically
contiguous chunk succeed, instead of failing with an invalid order.
This also avoids redundant "try-fail-degrade" cycles in
__smc_buf_create().

For SMCR_MIXED_BUFS, no cap is needed: if the order exceeds
MAX_PAGE_ORDER, alloc_pages() will silently fail (__GFP_NOWARN)
and automatically fall back to virtual memory.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>
---
Changes v2 -> v3:
https://lore.kernel.org/netdev/20260407124337.88128-1-alibuda@linux.alibaba.com/
Remove unnecessary parentheses
Changes v1 -> v2:
https://lore.kernel.org/netdev/20260312082154.36971-1-alibuda@linux.alibaba.com/
---
 net/smc/smc_core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index e2d083daeb7e..cf6b620fef05 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -2440,6 +2440,10 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb)
 		/* use socket send buffer size (w/o overhead) as start value */
 		bufsize = smc->sk.sk_sndbuf / 2;
 
+	/* limit bufsize for physically contiguous buffers */
+	if (!is_smcd && lgr->buf_type == SMCR_PHYS_CONT_BUFS)
+		bufsize = min_t(int, bufsize, PAGE_SIZE << MAX_PAGE_ORDER);
+
 	for (bufsize_comp = smc_compress_bufsize(bufsize, is_smcd, is_rmb);
 	     bufsize_comp >= 0; bufsize_comp--) {
 		if (is_rmb) {
-- 
2.45.0

Re: [PATCH net-next v3] net/smc: cap allocation order for SMC-R physically contiguous buffers

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 29 Apr 2026 10:16:37 +0800 you wrote:
> The alloc_pages() 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, cap the allocation order to MAX_PAGE_ORDER.
> This ensures the attempts to allocate the largest possible physically
> contiguous chunk succeed, instead of failing with an invalid order.
> This also avoids redundant "try-fail-degrade" cycles in
> __smc_buf_create().
> 
> [...]

Here is the summary with links:
  - [net-next,v3] net/smc: cap allocation order for SMC-R physically contiguous buffers
    https://git.kernel.org/netdev/net-next/c/4cc5130ee84a

You are awesome, thank you!
-- 
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