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Re: [PATCH 2/3] x86/EFI: replace ebmalloc()
- To: Marek Marczykowski <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 13 Nov 2025 13:53:40 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Daniel Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 13 Nov 2025 12:53:45 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13.11.2025 13:40, Marek Marczykowski wrote:
> On Thu, Nov 13, 2025 at 12:09:37PM +0100, Jan Beulich wrote:
>> Use the new brk_alloc() instead, with ebmalloc() merely being a thin
>> wrapper.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> I'm not quite certain whether we ought to permit non-page-granular
>> reservations. The in-memory image being somewhat larger due to possibly
>> excessive padding isn't really a big problem, I think.
>
> My grep says ebmalloc is used in just two places:
> 1. For efi_memmap (via efi_arch_allocate_mmap_buffer())
> 2. For various cmdline options and module names (via aplace_string())
>
> The second one is probably undesirable to allocate full page for each
> one. On the other hand, the current approach (putting small allocations
> at the same page as an earlier page-aligned one) also has its issues -
> see comments on 3/3 patch.
Imo if such sharing of a page is unwanted, then it's the side caring about
the non-sharing which ought to request an exact multiple of pages. Wasting
space due to doing this in the BRK implementation is undesirable.
Jan
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