linux-kernel - Re: [PATCH v1 01/29] mm/balloon_compaction: we cannot have isolated pages in the balloon list

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Message-ID: <542cdfda-b90b-4a1a-8001-ae028b9a039a@lucifer.local>
Date: Mon, 30 Jun 2025 15:45:45 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
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Subject: Re: [PATCH v1 01/29] mm/balloon_compaction: we cannot have isolated
 pages in the balloon list

On Mon, Jun 30, 2025 at 02:59:42PM +0200, David Hildenbrand wrote:
> The core will set PG_isolated only after mops->isolate_page() was
> called. In case of the balloon, that is where we will remove it from
> the balloon list. So we cannot have isolated pages in the balloon list.

Indeed, I see isolate_movable_ops_page() is the only place the beautiful +
consistent macro SetPageMovableOpsIsolated() is invoked, and
balloon_page_isolate() invokes list_del(&page->lru).

The only case it doesn't do that is one where it returns false so the flag
wouldn't be set.

>
> Let's drop this unnecessary check.
>
> Acked-by: Zi Yan <ziy@...dia.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

So,

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  mm/balloon_compaction.c | 6 ------
>  1 file changed, 6 deletions(-)
>
> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> index d3e00731e2628..fcb60233aa35d 100644
> --- a/mm/balloon_compaction.c
> +++ b/mm/balloon_compaction.c
> @@ -94,12 +94,6 @@ size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
>  		if (!trylock_page(page))
>  			continue;
>
> -		if (IS_ENABLED(CONFIG_BALLOON_COMPACTION) &&
> -		    PageIsolated(page)) {
> -			/* raced with isolation */
> -			unlock_page(page);
> -			continue;
> -		}
>  		balloon_page_delete(page);
>  		__count_vm_event(BALLOON_DEFLATE);
>  		list_add(&page->lru, pages);
> --
> 2.49.0
>