linux-kernel - Re: [PATCH 3/6] mm: page_alloc: move free pages when converting block during isolation

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Date:   Mon, 11 Sep 2023 16:17:07 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] mm: page_alloc: move free pages when converting block
 during isolation

On 11 Sep 2023, at 15:41, Johannes Weiner wrote:

> When claiming a block during compaction isolation, move any remaining
> free pages to the correct freelists as well, instead of stranding them
> on the wrong list. Otherwise, this encourages incompatible page mixing
> down the line, and thus long-term fragmentation.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> ---
>  mm/page_alloc.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3db405414174..f6f658c3d394 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2548,9 +2548,12 @@ int __isolate_free_page(struct page *page, unsigned int order)
>  			 * Only change normal pageblocks (i.e., they can merge
>  			 * with others)
>  			 */
> -			if (migratetype_is_mergeable(mt))
> +			if (migratetype_is_mergeable(mt)) {
>  				set_pageblock_migratetype(page,
>  							  MIGRATE_MOVABLE);
> +				move_freepages_block(zone, page,
> +						     MIGRATE_MOVABLE, NULL);
> +			}
>  		}
>  	}
>
> -- 
> 2.42.0

Is this needed? And is this correct?

__isolate_free_page() removes the free page from a free list, but the added
move_freepages_block() puts the page back to another free list, making
__isolate_free_page() not do its work. OK. the for loop is going through
the pages within the pageblock, so move_freepages_block() should be used
on the rest of the pages on the pageblock.

So to make this correct, the easies change might be move
del_page_from_free_list(page, zone, order) below this code chunk.

--
Best Regards,
Yan, Zi

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