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authorKees Cook <kees+treewide@kernel.org>2026-09-02 15:31:14 -0700
committerKees Cook <kees@kernel.org>2026-09-04 21:37:00 -0700
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treec65086f9bdcd48c6360fb7cb4598bca084da1f32 /Documentation/networking/smc-sysctl.rst
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treewide: refresh kmalloc_obj() conversionsgrafted
This is another run of the Coccinelle script for converting kmalloc() family of allocations to kmalloc_obj() via the existing rules in scripts/coccinelle/api/kmalloc_objs.cocci This catches both the set of kmalloc() uses added since the first kmalloc_obj() conversions in v7.0 and adds a large group missed in the first pass due to Coccinelle not interacting well with the cleanup.h scoped_...() family of macros[1]. I worked around this with spatch's "--macro-file" argument to a file with all the scoped_...() macros mapped to Coccinelle's YACFE_ITERATOR[2] as that was the closest viable control flow indicator I could find. Build tested allmodconfig on x86, arm64, arm, loongarch, mips, powerpc, riscv, and s390 with no new warnings. Link: https://lore.kernel.org/lkml/202609021314.8A9C0B8@keescook/ [1] Link: https://github.com/coccinelle/coccinelle/blob/master/standard.h [2] Signed-off-by: Kees Cook <kees+treewide@kernel.org>
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+.. SPDX-License-Identifier: GPL-2.0
+
+==========
+SMC Sysctl
+==========
+
+/proc/sys/net/smc/* Variables
+=============================
+
+autocorking_size - INTEGER
+ Setting SMC auto corking size:
+ SMC auto corking is like TCP auto corking from the application's
+ perspective of view. When applications do consecutive small
+ write()/sendmsg() system calls, we try to coalesce these small writes
+ as much as possible, to lower total amount of CDC and RDMA Write been
+ sent.
+ autocorking_size limits the maximum corked bytes that can be sent to
+ the under device in 1 single sending. If set to 0, the SMC auto corking
+ is disabled.
+ Applications can still use TCP_CORK for optimal behavior when they
+ know how/when to uncork their sockets.
+
+ Default: 64K
+
+smcr_buf_type - INTEGER
+ Controls which type of sndbufs and RMBs to use in later newly created
+ SMC-R link group. Only for SMC-R.
+
+ Default: 0 (physically contiguous sndbufs and RMBs)
+
+ Possible values:
+
+ - 0 - Use physically contiguous buffers
+ - 1 - Use virtually contiguous buffers
+ - 2 - Mixed use of the two types. Try physically contiguous buffers first.
+ If not available, use virtually contiguous buffers then.
+
+smcr_testlink_time - INTEGER
+ How frequently SMC-R link sends out TEST_LINK LLC messages to confirm
+ viability, after the last activity of connections on it. Value 0 means
+ disabling TEST_LINK.
+
+ Default: 30 seconds.
+
+wmem - INTEGER
+ Initial size of send buffer used by SMC sockets.
+
+ The minimum value is 16KiB and there is no hard limit for max value, but
+ only allowed 512KiB for SMC-R and 1MiB for SMC-D.
+
+ Default: 64KiB
+
+rmem - INTEGER
+ Initial size of receive buffer (RMB) used by SMC sockets.
+
+ The minimum value is 16KiB and there is no hard limit for max value, but
+ only allowed 512KiB for SMC-R and 1MiB for SMC-D.
+
+ Default: 64KiB
+
+smcr_max_links_per_lgr - INTEGER
+ Controls the max number of links can be added to a SMC-R link group. Notice that
+ the actual number of the links added to a SMC-R link group depends on the number
+ of RDMA devices exist in the system. The acceptable value ranges from 1 to 2. Only
+ for SMC-R v2.1 and later.
+
+ Default: 2
+
+smcr_max_conns_per_lgr - INTEGER
+ Controls the max number of connections can be added to a SMC-R link group. The
+ acceptable value ranges from 16 to 255. Only for SMC-R v2.1 and later.
+
+ Default: 255
+
+smcr_max_send_wr - INTEGER
+ So-called work request buffers are SMCR link (and RDMA queue pair) level
+ resources necessary for performing RDMA operations. Since up to 255
+ connections can share a link group and thus also a link and the number
+ of the work request buffers is decided when the link is allocated,
+ depending on the workload it can be a bottleneck in a sense that threads
+ have to wait for work request buffers to become available. Before the
+ introduction of this control the maximal number of work request buffers
+ available on the send path used to be hard coded to 16. With this control
+ it becomes configurable. The acceptable range is between 2 and 2048.
+
+ 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 keep retrying
+ with half of the buffer count until it is either 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
+
+smcr_max_recv_wr - INTEGER
+ So-called work request buffers are SMCR link (and RDMA queue pair) level
+ resources necessary for performing RDMA operations. Since up to 255
+ connections can share a link group and thus also a link and the number
+ of the work request buffers is decided when the link is allocated,
+ depending on the workload it can be a bottleneck in a sense that threads
+ have to wait for work request buffers to become available. Before the
+ introduction of this control the maximal number of work request buffers
+ available on the receive path used to be hard coded to 48. With this control
+ it becomes configurable. The acceptable range is between 2 and 2048.
+
+ 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 keep retrying
+ with half of the buffer count until it is either successful or (unlikely)
+ we dip below the old hard coded value which is 48 where we give up much
+ like before having this control.
+
+ Default: 48
+
+limit_smc_hs - INTEGER
+ Whether to limit SMC handshake for newly created sockets.
+
+ When enabled, SMC listen path applies handshake limitation based on
+ handshake worker congestion and queued SMC handshake load.
+
+ Possible values:
+
+ - 0 - Disable handshake limitation
+ - 1 - Enable handshake limitation
+
+ Default: 0 (disable)
+
+hs_ctrl - STRING
+ Select the SMC handshake control profile by name.
+
+ This string refers to the name of a user-implemented
+ BPF struct_ops instance of type smc_hs_ctrl.
+
+ The selected profile controls whether SMC options are advertised
+ during TCP SYN/SYN-ACK handshake.
+
+ Only available when CONFIG_SMC_HS_CTRL_BPF is enabled.
+ Write an empty string to clear the current profile.
+
+ Default: empty string