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Re: [PATCH v9 6/8] xen/arm: unpopulate memory when domain is static
- To: Penny Zheng <Penny.Zheng@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 25 Jul 2022 17:35:30 +0200
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- Cc: wei.chen@xxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 25 Jul 2022 15:35:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.07.2022 07:46, Penny Zheng wrote:
> Today when a domain unpopulates the memory on runtime, they will always
> hand the memory back to the heap allocator. And it will be a problem if domain
> is static.
>
> Pages as guest RAM for static domain shall be reserved to only this domain
> and not be used for any other purposes, so they shall never go back to heap
> allocator.
>
> This commit puts reserved pages on the new list resv_page_list only after
> having taken them off the "normal" list, when the last ref dropped.
I guess this wording somehow relates to ...
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -2674,10 +2674,14 @@ void free_domstatic_page(struct page_info *page)
>
> drop_dom_ref = !domain_adjust_tot_pages(d, -1);
>
> - spin_unlock_recursive(&d->page_alloc_lock);
> -
> free_staticmem_pages(page, 1, scrub_debug);
>
> + /* Add page on the resv_page_list *after* it has been freed. */
> + if ( !drop_dom_ref )
> + page_list_add_tail(page, &d->resv_page_list);
... the conditional used here. I cannot, however, figure why there is
this conditional (and said part of the description also doesn't help
me figure it out).
As an aside: A title prefix of xen/arm: suggests you're mostly
touching Arm code. But you're touching exclusively common code here.
I for one would almost have skipped this patch (more than once) when
deciding which ones (may) want me looking at them.
Jan
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