[PATCH net-next v2] net/smc: cap allocation order for SMC-R physically contiguous buffers

[PATCH net-next v2] 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>
---
Changes v1 -> v2:
https://lore.kernel.org/netdev/20260312082154.36971-1-alibuda@linux.alibaba.com/

- Move the bufsize cap from smcr_new_buf_create() up to
  __smc_buf_create(), which is simpler and avoids touching
  the allocation logic itself.
---
 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..cdd881746e21 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