[PATCH net-next 0/6] net/smc: Introduce virtually contiguous buffers for SMC-R

Wen Gu
2022-07-12T11:51:49Z

On long-running enterprise production servers, high-order contiguous
memory pages are usually very rare and in most cases we can only get
fragmented pages.

When replacing TCP with SMC-R in such production scenarios, attempting
to allocate high-order physically contiguous sndbufs and RMBs may result
in frequent memory compaction, which will cause unexpected hung issue
and further stability risks.

So this patch set is aimed to allow SMC-R link group to use virtually
contiguous sndbufs and RMBs to avoid potential issues mentioned above.
Whether to use physically or virtually contiguous buffers can be set
by sysctl smcr_buf_type.

Note that using virtually contiguous buffers will bring an acceptable
performance regression, which can be mainly divided into two parts:

1) regression in data path, which is brought by additional address
translation of sndbuf by RNIC in Tx. But in general, translating
address through MTT is fast. According to qperf test, this part
regression is basically less than 10% in latency and bandwidth.
(see patch 5/6 for details)

2) regression in buffer initialization and destruction path, which is
brought by additional MR operations of sndbufs. But thanks to link
group buffer reuse mechanism, the impact of this kind of regression
decreases as times of buffer reuse increases.

Patch set overview:
- Patch 1/6 and 2/6 mainly about simplifying and optimizing DMA sync
operation, which will reduce overhead on the data path, especially
when using virtually contiguous buffers;
- Patch 3/6 and 4/6 introduce a sysctl smcr_buf_type to set the type
of buffers in new created link group;
- Patch 5/6 allows SMC-R to use virtually contiguous sndbufs and RMBs,
including buffer creation, destruction, MR operation and access;
- patch 6/6 extends netlink attribute for buffer type of SMC-R link group;

Guangguan Wang (2):
net/smc: remove redundant dma sync ops
net/smc: optimize for smc_sndbuf_sync_sg_for_device and
smc_rmb_sync_sg_for_cpu

Wen Gu (4):
net/smc: Introduce a sysctl for setting SMC-R buffer type
net/smc: Use sysctl-specified types of buffers in new link group
net/smc: Allow virtually contiguous sndbufs or RMBs for SMC-R
net/smc: Extend SMC-R link group netlink attribute

include/net/netns/smc.h | 1 +
include/uapi/linux/smc.h | 1 +
net/smc/af_smc.c | 68 +++++++++++--
net/smc/smc_clc.c | 8 +-
net/smc/smc_clc.h | 2 +-
net/smc/smc_core.c | 246 ++++++++++++++++++++++++++++++-----------------
net/smc/smc_core.h | 20 +++-
net/smc/smc_ib.c | 44 +++++++--
net/smc/smc_ib.h | 2 +
net/smc/smc_llc.c | 33 ++++---
net/smc/smc_rx.c | 92 ++++++++++++++----
net/smc/smc_sysctl.c | 11 +++
net/smc/smc_tx.c | 10 +-
13 files changed, 391 insertions(+), 147 deletions(-)

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1.8.3.1