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centos 7.5 supermicro x11sta-t – when I set kernel parameter memmap= the kernel hangs on boot

I am using some middleware that expects memory to be reserved with the memmap= kernel parameter.

With centos 7.5 supermicro x11sta-t – when I set kernel parameter memmap= the kernel hangs on boot.

Is there some new limitation on this time-honored means of reserving a large contiguous array of memory for drivers to avoid scatter-gather?

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  1. Chosen as BEST ANSWER
    0

    My time-honored memory failed me yet again. I couldn't find my notes on the process and tried to work from memory.

    When configuring memmap= from /etc/default/grub, you MUST escape the '' and '$' characters on the command line. So if you want:

    memmap=64M$4G

    then you MUST use

    memmap=64M$4G

    in the /etc/default/grub file. This ends up being

    memmap=64M$4G

    in the grub menu, which will actually work.

    Don't fall in this hole that I seem to keep falling into...


  2. 0

    A note to @Nufosmatic’s answer.

    I am working on Fedora 36 and by default GRUB2 uses BootLoaderSpec (BLS). BLS uses blscfg command to read a .conf file in /boot/loader/entries/. It seems that $ is always eaten by blscfg regardless how many you add before it.

    So for @Nufosmatic’s solution to work, also disable BLS by setting GRUB_ENABLE_BLSCFG=false in /etc/default/grub, then generate a new grub.cfg by grub2-mkconfig -o /boot/grub2/grub.cfg.

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