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Re: [PATCH v2 1/3] x86: introduce "brk" allocator
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 28 Jul 2026 10:36:36 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Roger Pau Monné <roger@xxxxxxxxxxxxxx>
- Delivery-date: Tue, 28 Jul 2026 08:36:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 27.07.2026 12:19, Jan Beulich wrote:
> ... to replace ebmalloc(), and then to find further use(s) to allow
> recovering memory which is needed very early (and hence needs setting up
> statically), but may not fully be used (or not used at all).
>
> Note that unlike free_ebmalloc_unused_mem(), brk_free_unused() (once
> other code is converted) will be able to free part of the BRK space even
> in the xen.efi case. That would happen if BRK space extends across a 2Mb
> boundary, and actual use stops before that boundary.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Changing setup.c's reserve_e820_ram() uses would be cumbersome when done
> right here. That'll be done when ebmalloc() is replaced, and hence
> what's there can also simply be replaced.
>
> The xen.efi detection may want separating out into a helper.
>
> When linking xen.efi, ld produces a base relocation for the reference to
> __subsystem__, which is wrong (that's an absolute symbol, after all).
> While that will need fixing there, it does no harm for our purposes.
This remark is stale, I've updated it to:
"When linking xen.efi, GNU ld prior to 2.46 produces a base relocation for
the reference to __subsystem__, which is wrong (that's an absolute symbol,
after all). That does no harm for our purposes, though."
Jan
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