Re: [Xen-devel] [PATCH v2 2/2] x86/dom0: improve paging memory usage calculations

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Dec 05, 2018 at 03:55:00PM +0100, Roger Pau Monne wrote:
> Current approximation of paging memory usage is based on the required
> amount when running in shadow mode and doesn't take into account the
> memory required by the IOMMU page tables.
> 
> Fix this by introducing a function to calculate the amount of memory
> required by HAP/IOMMU page tables. The formula used to calculate such
> approximation is based on the pessimistic approach that each 4KB
> memory chunk will use 8 bytes of page table memory. Note that this
> approximation might need further tuning based on testing on different
> systems.
> 
> Also fix the calculation of the required paging related memory in
> dom0_compute_nr_pages to take into account the paging implementation
> (shadow or HAP) and whether the IOMMU pages tables are shared with the
> HAP page tables.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> Cc: andrei.semenov@xxxxxxxxx
> ---
>  xen/arch/x86/dom0_build.c        | 31 +++++++++++++++++++++++++++----
>  xen/arch/x86/hvm/dom0_build.c    |  6 ++++--
>  xen/include/asm-x86/dom0_build.h |  2 ++
>  3 files changed, 33 insertions(+), 6 deletions(-)
> 
> diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
> index ba9aa85611..3a8e138f23 100644
> --- a/xen/arch/x86/dom0_build.c
> +++ b/xen/arch/x86/dom0_build.c
> @@ -267,6 +267,25 @@ unsigned long __init dom0_shadow_pages(const struct 
> domain *d,
>      return ((memkb + 1023) / 1024) << (20 - PAGE_SHIFT);
>  }
>  
> +unsigned long __init dom0_hap_pages(const struct domain *d,
> +                                    unsigned long nr_pages)
> +{
> +    /*
> +     * Attempt to account for at least some of the MMIO regions by adding the
> +     * size of the holes in the memory map to the amount of pages to map. 
> Note
> +     * this will obviously not account for MMIO regions that are past the 
> last
> +     * RAM range in the memory map.
> +     */
> +    nr_pages += max_page - total_pages;

Do those regions past end of RAM range show up in E820 map? If so, why
not just sum up all reserved regions?

Wei.

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