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In commit 72653ae530 ("selftests: net: tcp_mmap:
Use huge pages in send path") I made a change to use hugepages
for the buffer used by the client (tx path)
Today, I understood that the cause for poor zerocopy
performance was that after a mmap() for a 512KB memory
zone, kernel uses a single zeropage, mapped 128 times.
This was really the reason for poor tx path performance
in zero copy mode, because this zero page refcount is
under high pressure, especially when TCP ACK packets
are processed on another cpu.
We need either to force a COW on all the memory range,
or use MAP_POPULATE so that a zero page is not abused.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230120181136.3764521-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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.