+ Mark S.

On Tue, May 19, 2020 at 04:34:50PM +0100, Peter Robinson wrote:
> > From: Prarit Bhargava <pra...@redhat.com>
> >
> > The internal make command 'make rh-brew'/'make dist-brew' is failing with
> >
> > Processing 
> > /home/prarit/git-kernel/kernel-ark/redhat/configs/kernel-aarch64-debug-fedora.config
> >  ... Error: Mismatches found in configuration files
> > Found CONFIG_FORCE_MAX_ZONEORDER=11 after generation, had 
> > CONFIG_FORCE_MAX_ZONEORDER=13 in Source tree
> >
> > ARK commit f5ca593e1c2e ("configs: Adjust CONFIG_FORCE_MAX_ZONEORDER for
> > Fedora") set this to 11, and follow-on ARK commit dd028d261347 ("[redhat]
> > Sync up ARK's Fedora config tree with Fedora's dist-git") erroneously
> > overwrote the value back to 13.
> >
> > Set CONFIG_FORCE_MAX_ZONEORDER back to 11 for aarch64.
> 
> For reference the reason we have this disparity goes back to why
> Fedora doesn't have 64K page sizes for aarch64. The reason is because
> with 64K pages it makes CMA 512Mb rather than the 64Mb (which I think
> can actually be 16) we have with 4K pages. I seem to remember its
> something to do with CMA using large pages and with 64K page sizes
> that makes the smallest large page to be 512Mb.
> 
> Losing 512Mb is obviously fatal on devices with small amounts of RAM
> like a bunch of the SBCs we support on Fedora so to support SBCs we
> had to move to 4K pages until we got a proper fix for this. Related it
> actually also affects RHEL for things like AWS images with small
> amounts of memory so I suspect it would be useful to be fixed in the
> RHEL use case too.

Thanks Peter for the context!

Mark should we enable this for ARK / RHEL-9?

> 
> Peter
> 
> > Fixes: dd028d261347 ("[redhat] Sync up ARK's Fedora config tree with 
> > Fedora's dist-git")
> > Signed-off-by: Prarit Bhargava <pra...@redhat.com>
> > Cc: ho...@redhat.com
> > Cc: jcl...@redhat.com
> > ---
> >  .../fedora/generic/arm/aarch64/CONFIG_FORCE_MAX_ZONEORDER       | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git 
> > a/redhat/configs/fedora/generic/arm/aarch64/CONFIG_FORCE_MAX_ZONEORDER 
> > b/redhat/configs/fedora/generic/arm/aarch64/CONFIG_FORCE_MAX_ZONEORDER
> > index b730690db048..8220d67904ea 100644
> > --- a/redhat/configs/fedora/generic/arm/aarch64/CONFIG_FORCE_MAX_ZONEORDER
> > +++ b/redhat/configs/fedora/generic/arm/aarch64/CONFIG_FORCE_MAX_ZONEORDER
> > @@ -1,4 +1,4 @@
> >  # We technically want this to be 13 for Fedora with 4K pages but that's 
> > only
> >  # an option with an out of tree patch. Keep this 11 for compatibility until
> >  # we figure out what we want here
> > -CONFIG_FORCE_MAX_ZONEORDER=13
> > +CONFIG_FORCE_MAX_ZONEORDER=11
> > --
> > 2.26.2
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