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Re: [PATCH 2/2] xen/mm: reset PFN_ORDER for offlined buddy heads
- To: Bernhard Kaindl <bernhard.kaindl@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 2 Jun 2026 17:57:34 +0200
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- Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 02 Jun 2026 15:57:46 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 28.05.2026 16:58, Bernhard Kaindl wrote:
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -1485,6 +1485,13 @@ static int reserve_offlined_page(struct page_info
> *head)
> ASSERT(node_avail_pages[node] > 0);
> node_avail_pages[node]--;
>
> + /*
> + * All offlined pages are standalone pages: If this offlined page was
> + * the head of a higher-order buddy, we need to reset its order to 0:
> + */
> + if ( cur_head == head && head_order != 0 )
> + PFN_ORDER(cur_head) = 0;
> +
> page_list_add_tail(cur_head,
> test_bit(_PGC_broken, &cur_head->count_info) ?
> &page_broken_list : &page_offlined_list);
Again, with this separated from and moved ahead of the new test:
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
I'd suggest to drop the rhs of the && though: There's nothing wrong with storing
0 when the field already is 0. I actually wonder whether the if() is needed at
all. Unconditionally storing 0 is going to make the code more robust against
future changes elsewhere.
Jan
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