Re: [PATCH] xen/x86: add extra pages to unpopulated-alloc if available

[Jürgen Groß <jgross@xxxxxxxx>]

On 29.04.24 17:50, Roger Pau Monne wrote:
> Commit 262fc47ac174 ('xen/balloon: don't use PV mode extra memory for zone
> device allocations') removed the addition of the extra memory ranges to the
> unpopulated range allocator, using those only for the balloon driver.
>
> This forces the unpopulated allocator to attach hotplug ranges even when spare
> memory (as part of the extra memory ranges) is available.  Furthermore, on PVH
> domains it defeats the purpose of commit 38620fc4e893 ('x86/xen: attempt to
> inflate the memory balloon on PVH'), as extra memory ranges would only be
> used to map foreign memory if the kernel is built without XEN_UNPOPULATED_ALLOC
> support.
>
> Fix this by adding a helpers that adds the extra memory ranges to the list of
> unpopulated pages, and zeroes the ranges so they are not also consumed by the
> balloon driver.
>
> This should have been part of 38620fc4e893, hence the fixes tag.
>
> Note the current logic relies on unpopulated_init() (and hence
> arch_xen_unpopulated_init()) always being called ahead of balloon_init(), so
> that the extra memory regions are consumed by arch_xen_unpopulated_init().
>
> Fixes: 38620fc4e893 ('x86/xen: attempt to inflate the memory balloon on PVH')
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen