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Xuan Zhuo says:
====================
virtio_net: rx enable premapped mode by default
Actually, for the virtio drivers, we can enable premapped mode whatever
the value of use_dma_api. Because we provide the virtio dma apis.
So the driver can enable premapped mode unconditionally.
This patch set makes the big mode of virtio-net to support premapped mode.
And enable premapped mode for rx by default.
Based on the following points, we do not use page pool to manage these
pages:
1. virtio-net uses the DMA APIs wrapped by virtio core. Therefore,
we can only prevent the page pool from performing DMA operations, and
let the driver perform DMA operations on the allocated pages.
2. But when the page pool releases the page, we have no chance to
execute dma unmap.
3. A solution to #2 is to execute dma unmap every time before putting
the page back to the page pool. (This is actually a waste, we don't
execute unmap so frequently.)
4. But there is another problem, we still need to use page.dma_addr to
save the dma address. Using page.dma_addr while using page pool is
unsafe behavior.
5. And we need space the chain the pages submitted once to virtio core.
More:
https://lore.kernel.org/all/CACGkMEu=Aok9z2imB_c5qVuujSh=vjj1kx12fy9N7hqyi+M5Ow@mail.gmail.com/
Why we do not use the page space to store the dma?
http://lore.kernel.org/all/CACGkMEuyeJ9mMgYnnB42=hw6umNuo=agn7VBqBqYPd7GN=+39Q@mail.gmail.com
====================
Link: https://lore.kernel.org/r/20240511031404.30903-1-xuanzhuo@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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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 reStructuredText 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.