Re: [PATCH 3/4] mm: page_alloc: move capture_control to the page allocator

[Johannes Weiner <hannes@cmpxchg.org>]

On Thu, Jul 02, 2026 at 12:20:48PM +0200, Vlastimil Babka (SUSE) wrote:
> Now my version (only compile tested):

Ah, now I get it. Thanks.

> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index f29ef0653546..66a2f70e9e01 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -58,6 +58,7 @@ enum compact_result {
>  };
>  
>  struct alloc_context; /* in mm/internal.h */
> +struct capture_control; /* in mm/internal.h */
>  
>  /*
>   * Number of free order-0 pages that should be available above given watermark
> @@ -92,7 +93,7 @@ extern int fragmentation_index(struct zone *zone, unsigned int order);
>  extern enum compact_result try_to_compact_pages(gfp_t gfp_mask,
>  		unsigned int order, unsigned int alloc_flags,
>  		const struct alloc_context *ac, enum compact_priority prio,
> -		struct page **page);
> +		struct capture_control *capc);
>  extern void reset_isolation_suitable(pg_data_t *pgdat);
>  extern bool compaction_suitable(struct zone *zone, int order,
>  				unsigned long watermark, int highest_zoneidx);
> diff --git a/mm/compaction.c b/mm/compaction.c
> index b7878e4a2c4b..902573797f99 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -2792,7 +2792,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
>  static enum compact_result compact_zone_order(struct zone *zone, int order,
>  		gfp_t gfp_mask, enum compact_priority prio,
>  		unsigned int alloc_flags, int highest_zoneidx,
> -		struct page **capture)
> +		struct capture_control *capc)
>  {
>  	enum compact_result ret;
>  	struct compact_control cc = {
> @@ -2809,36 +2809,8 @@ static enum compact_result compact_zone_order(struct zone *zone, int order,
>  		.ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
>  		.ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
>  	};
> -	struct capture_control capc = {
> -		.cc = &cc,
> -		.page = NULL,
> -	};
> -
> -	/*
> -	 * Make sure the structs are really initialized before we expose the
> -	 * capture control, in case we are interrupted and the interrupt handler
> -	 * frees a page.
> -	 */
> -	barrier();
> -	WRITE_ONCE(current->capture_control, &capc);
>  
> -	ret = compact_zone(&cc, &capc);
> -
> -	/*
> -	 * Make sure we hide capture control first before we read the captured
> -	 * page pointer, otherwise an interrupt could free and capture a page
> -	 * and we would leak it.
> -	 */
> -	WRITE_ONCE(current->capture_control, NULL);
> -	*capture = READ_ONCE(capc.page);
> -	/*
> -	 * Technically, it is also possible that compaction is skipped but
> -	 * the page is still captured out of luck(IRQ came and freed the page).
> -	 * Returning COMPACT_SUCCESS in such cases helps in properly accounting
> -	 * the COMPACT[STALL|FAIL] when compaction is skipped.
> -	 */
> -	if (*capture)
> -		ret = COMPACT_SUCCESS;
> +	ret = compact_zone(&cc, capc);

&capc, and I switched it to just return compact_zone(&cc, &capc);

But otherwise it looks clean to me. I'd just take this as-is with your
From: if you don't mind. Can I add your S-O-B?