linux-kernel - Re: [PATCH v1 3/6] mm/page_isolation: drop WARN_ON_ONCE() in set_migratetype

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Date:   Wed, 29 Jul 2020 21:24:10 +0800
From:   Baoquan He <bhe@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Michael S . Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v1 3/6] mm/page_isolation: drop WARN_ON_ONCE() in
 set_migratetype_isolate()

On 06/30/20 at 04:26pm, David Hildenbrand wrote:
> Inside has_unmovable_pages(), we have a comment describing how unmovable
> data could end up in ZONE_MOVABLE - via "movable_core". Also, besides
					  ~~~ 'movablecore'
> checking if the first page in the pageblock is reserved, we don't
> perform any further checks in case of ZONE_MOVABLE.
> 
> In case of memory offlining, we set REPORT_FAILURE, properly
> dump_page() the page and handle the error gracefully.
> alloc_contig_pages() users currently never allocate from ZONE_MOVABLE.
> E.g., hugetlb uses alloc_contig_pages() for the allocation of gigantic
> pages only, which will never end up on the MOVABLE zone
> (see htlb_alloc_mask()).
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  mm/page_isolation.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 553b49a34cf71..02a01bff6b219 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -58,16 +58,12 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
>  	spin_unlock_irqrestore(&zone->lock, flags);
>  	if (!ret) {
>  		drain_all_pages(zone);
> -	} else {
> -		WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> -
> -		if ((isol_flags & REPORT_FAILURE) && unmovable)
> -			/*
> -			 * printk() with zone->lock held will likely trigger a
> -			 * lockdep splat, so defer it here.
> -			 */
> -			dump_page(unmovable, "unmovable page");
> -	}
> +	} else if ((isol_flags & REPORT_FAILURE) && unmovable)

This else if branch should be enclosed in brace?

> +		/*
> +		 * printk() with zone->lock held will likely trigger a
> +		 * lockdep splat, so defer it here.
> +		 */
> +		dump_page(unmovable, "unmovable page");
>  
>  	return ret;
>  }

Otherwise, the patch looks good to me.

Reviewed-by: Baoquan He <bhe@...hat.com>