[ZGC] [aarch64] Unable to allocate heap for certain Linux kernel configurations

[Christoph Göttschkes]

On 2020-09-02 17:59, Stuart Monteith wrote:
> Hi,
>      You approach + Stefan's comments looks reasonable to me . I tested 
> your solution standalone on a Raspbery Pi 4 with 39 bit VA and on a 
> workstation with 48-bit addressing.
> 
> The configurations we support in Linux on arch64 are:
>      4KB pages: 39, 48 bits.
>      16KB pages: 36, 47, 48 bits
>      64KB pages:  42, 48, 52 bits.
> 
> Only the 4KB and 64KB configurations are worth considering, I don't 
> believe there are 16KB page configurations out there, so you could cut 
> the range down to a 52 to 39 bits search.
> 
> For completeness I should mention that this potentially could be cross 
> platform code. 5-level paging was added to x86, so they will have 57 
> bits available. ppc/s390x don't have ZGC ports yet.
> 
> My advice would be to stick with 48 bits for now, as there may be extra 
> considerations with the 52/57 bit address spaces.

Thanks for looking into this. I am about to post my RFR for this bug. I 
already included some of your suggestions (with some slight 
differences), but let's continue the discussion in the RFR thread.

-- Christoph