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Wen Gu says: ==================== net/smc: Introduce virtually contiguous buffers for SMC-R 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; v1->v2: - Patch 5/6 fixes build issue on 32bit; - Patch 3/6 adds description of new sysctl in smc-sysctl.rst; ==================== Signed-off-by: David S. Miller <davem@davemloft.net> |
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README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.