linux-kernel - Re: [PATCH v1 03/29] mm/zsmalloc: drop PageIsolated() related VM_BUG

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Message-ID: <ccc333aa-46c2-49ae-8d0f-ffbde95cb22d@lucifer.local>
Date: Mon, 30 Jun 2025 16:17:53 +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 03/29] mm/zsmalloc: drop PageIsolated() related
 VM_BUG_ONs

On Mon, Jun 30, 2025 at 02:59:44PM +0200, David Hildenbrand wrote:
> Let's drop these checks; these are conditions the core migration code
> must make sure will hold either way, no need to double check.
>
> Acked-by: Zi Yan <ziy@...dia.com>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> Acked-by: Harry Yoo <harry.yoo@...cle.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

LGTM, one comment below.

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

> ---
>  mm/zpdesc.h   | 5 -----
>  mm/zsmalloc.c | 5 -----
>  2 files changed, 10 deletions(-)
>
> diff --git a/mm/zpdesc.h b/mm/zpdesc.h
> index d3df316e5bb7b..5cb7e3de43952 100644
> --- a/mm/zpdesc.h
> +++ b/mm/zpdesc.h
> @@ -168,11 +168,6 @@ static inline void __zpdesc_clear_zsmalloc(struct zpdesc *zpdesc)
>  	__ClearPageZsmalloc(zpdesc_page(zpdesc));
>  }
>
> -static inline bool zpdesc_is_isolated(struct zpdesc *zpdesc)
> -{
> -	return PageIsolated(zpdesc_page(zpdesc));
> -}
> -
>  static inline struct zone *zpdesc_zone(struct zpdesc *zpdesc)
>  {
>  	return page_zone(zpdesc_page(zpdesc));
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 999b513c7fdff..7f1431f2be98f 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1719,8 +1719,6 @@ static bool zs_page_isolate(struct page *page, isolate_mode_t mode)
>  	 * Page is locked so zspage couldn't be destroyed. For detail, look at
>  	 * lock_zspage in free_zspage.
>  	 */
> -	VM_BUG_ON_PAGE(PageIsolated(page), page);
> -
>  	return true;
>  }
>
> @@ -1739,8 +1737,6 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
>  	unsigned long old_obj, new_obj;
>  	unsigned int obj_idx;
>
> -	VM_BUG_ON_PAGE(!zpdesc_is_isolated(zpdesc), zpdesc_page(zpdesc));
> -
>  	/* The page is locked, so this pointer must remain valid */
>  	zspage = get_zspage(zpdesc);
>  	pool = zspage->pool;
> @@ -1811,7 +1807,6 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
>
>  static void zs_page_putback(struct page *page)
>  {
> -	VM_BUG_ON_PAGE(!PageIsolated(page), page);
>  }

Can we just drop zs_page_putback from movable_operations() now this is empty?

>
>  static const struct movable_operations zsmalloc_mops = {
> --
> 2.49.0
>