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Russell King says: ==================== net: mvneta: reduce size of TSO header allocation With reference to https://forum.turris.cz/t/random-kernel-exceptions-on-hbl-tos-7-0/18865/ https://github.com/openwrt/openwrt/pull/12375#issuecomment-1528842334 It appears that mvneta attempts an order-6 allocation for the TSO header memory. While this succeeds early on in the system's life time, trying order-6 allocations later can result in failure due to memory fragmentation. Firstly, the reason it's so large is that we take the number of transmit descriptors, and allocate a TSO header buffer for each, and each TSO header is 256 bytes. The driver uses a simple mechanism to determine the address - it uses the transmit descriptor index as an index into the TSO header memory. (The first obvious question is: do there need to be this many? Won't each TSO header always have at least one bit of data to go with it? In other words, wouldn't the maximum number of TSO headers that a ring could accept be the number of ring entries divided by 2?) There is no real need for this memory to be an order-6 allocation, since nothing in hardware requires this buffer to be contiguous. Therefore, this series splits this order-6 allocation up into 32 order-1 allocations (8k pages on 4k page platforms), each giving 32 TSO headers per page. In order to do this, these patches: 1) fix a horrible transmit path error-cleanup bug - the existing code unmaps from the first descriptor that was allocated at interface bringup, not the first descriptor that the packet is using, resulting in the wrong descriptors being unmapped. 2) since xdp support was added, we now have buf->type which indicates what this transmit buffer contains. Use this to mark TSO header buffers. 3) get rid of IS_TSO_HEADER(), instead using buf->type to determine whether this transmit buffer needs to be DMA-unmapped. 4) move tso_build_hdr() into mvneta_tso_put_hdr() to keep all the TSO header building code together. 5) split the TSO header allocation into chunks of order-1 pages. This has now been tested by the Turris folk and has been found to fix the allocation error. ==================== Link: https://lore.kernel.org/r/ZFtuhJOC03qpASt2@shell.armlinux.org.uk Signed-off-by: Paolo Abeni <pabeni@redhat.com> |
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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 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.