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bgmac allocates new replacement buffer before handling each received frame. Allocating & DMA-preparing 9724 B each time consumes a lot of CPU time. Ideally bgmac should just respect currently set MTU but it isn't the case right now. For now just revert back to the old limited frame size. This change bumps NAT masquerade speed by ~95%. Since commit8218f62c9c("mm: page_frag: use initial zero offset for page_frag_alloc_align()"), the bgmac driver fails to open its network interface successfully and runs out of memory in the following call stack: bgmac_open -> bgmac_dma_init -> bgmac_dma_rx_skb_for_slot -> netdev_alloc_frag BGMAC_RX_ALLOC_SIZE = 10048 and PAGE_FRAG_CACHE_MAX_SIZE = 32768. Eventually we land into __page_frag_alloc_align() with the following parameters across multiple successive calls: __page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=0 __page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=10048 __page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=20096 __page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=30144 So in that case we do indeed have offset + fragsz (40192) > size (32768) and so we would eventually return NULL. Reverting to the older 1500 bytes MTU allows the network driver to be usable again. Fixes:8c7da63978("bgmac: configure MTU and add support for frames beyond 8192 byte size") Signed-off-by: Rafał Miłecki <rafal@milecki.pl> [florian: expand commit message about recent commits] Reviewed-by: Simon Horman <horms@kernel.org> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com> Link: https://patch.msgid.link/20250127175159.1788246-1-florian.fainelli@broadcom.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 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.