ACK/cmnt: [SRU][F/raspi][PATCH 0/1] Large Page support disabled on Raspberry Pi kernels (LP: #1933532)

[Joseph Salisbury]

Testing does show TLB miss improvement in bug report.

The annotations file change references bug LP:1933627, which is a bug 
for Hirsute and Impish.  Should the change reference the Focal bug? 
(1933532) like:
'mark<ENFORCE> note<LP: #1933532>'


Acked-by: Joseph Salisbury <joseph.salisbury at canonical.com>


On 1/21/22 08:41, Juerg Haefliger wrote:
> Enable hugepages and hugetlb for Focal raspi 5.4 to match the main arm kernels
> and later raspi kernels. This is reasonable given that there are Pi 4 devices
> with up to 8GB of memory.
>
> [ Impact ]
>
> It appears that large page support and transparent hugepages are disabled in config on the Raspberry Pi. It would be nice if they were enabled in the kernel configuration, even if they are disabled by default. Then they could be set in user-editable config via the "transparent_hugepage" boot option.
>
> With 4GB hardware in this family, there might be valid uses for large pages.
>
> root at ubuntu:/home/ubuntu# hugeadm --explain
> hugeadm:ERROR: kernel does not support huge pages
>
> root at ubuntu:/home/ubuntu# lsb_release -a
> No LSB modules are available.
> Distributor ID: Ubuntu
> Description:    Ubuntu 20.04.2 LTS
> Release:        20.04
> Codename:       focal
>
> root at ubuntu:/home/ubuntu# uname -a
> Linux ubuntu 5.4.0-1038-raspi #41-Ubuntu SMP PREEMPT Thu Jun 17 14:14:11 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux
>
> root at ubuntu:/home/ubuntu# grep -i huge /boot/config-5.4.0-1038-raspi
> CONFIG_SYS_SUPPORTS_HUGETLBFS=y
> CONFIG_ARCH_WANT_HUGE_PMD_SHARE=y
> CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y
> CONFIG_HAVE_ARCH_HUGE_VMAP=y
> # CONFIG_TRANSPARENT_HUGEPAGE is not set
> # CONFIG_HUGETLBFS is not set
>
> [ Test Case ]
>
> See above:
>
> [ Fix ]
>
> Enable HUGETLBFS and TRANSPARENT_HUGEPAGE to match the master kernel and hirsure and later raspi kernels.
>
> [ Where Problems Could Occur ]
>
> Thess configs enable code that is disabled by default. However, there is minimal stub code running at boot so problems would most likely show up as splats during boot or later on when hugetlbfs is explicitly mounted by systemd.
>
> Juerg Haefliger (1):
>    UBUNTU: [Config] raspi: Set HUGETLBFS=y and TRANSPARENT_HUGEPAGE=y
>
>   debian.raspi/config/annotations          |  8 ++++----
>   debian.raspi/config/config.common.ubuntu | 13 +++++++++++--
>   2 files changed, 15 insertions(+), 6 deletions(-)
>