Re: Small highmem segment with 32bit gnumach

On Thu, Sep 25, 2025 at 11:12:34PM +0100, João Pedro Malhado wrote:
> As Mike has outline recently, if a system has 1 GB of RAM one will end up with a
> 141MB highmem segment. This prevents booting the hurd with rumpdisk as he
> described, but the problems run deeper than that. Even booting the system using
> the ide drivers in gnumach, the system is sluggish, takes a long time to perform
> certain tasks, and can become unresponsive. The system becomes unresponsive
> for example while upgrading the hurd package, which  while setting up the
> translators launches rumpdisk (I think because of the detected USB ports). I
> don't think this is related to rumpdisk per se, but how gnumach is managing
> memory.
> In comparison, a laptop with 512MB of RAM runs much more smoothly than one with
> 1024MB!
> Is this because only the highmem segment with 141MB is being used for the
> user space?
> It was mentioned that it is not worth investing time in fixing the 32bit kernel,
> but I wonder if there is some sort of workaround. Is it possible to limit the
> amount of memory that is "shown to" gnumach such that it maps only the directmap
> segment and ignores the extra 141MB? Reading some old documentation I
> saw the uppemem option in grub, but this did not change anything (or I did not
> use it correctly).
> Is there a gnumach boot option that would work like mem=XX in linux?
> Or would anyone be able to suggest a patch for gnumach to just ignore the
> highmem segment which I could apply?

Hello,

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