linux-kernel - Re: [PATCH] mm/compaction: do not break pages whose order is larger than target order

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Message-ID: <8905cbf7-7507-44de-8721-b3e75e80732b@linux.alibaba.com>
Date: Fri, 25 Apr 2025 14:53:27 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Wenchao Hao <haowenchao22@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/compaction: do not break pages whose order is larger
 than target order



On 2025/4/24 23:38, Wenchao Hao wrote:
> When scanning free pages for memory compaction, if the compaction target
> order is explicitly specified, do not split pages in buddy whose order
> are larger than compaction target order.

We've already checked this in suitable_migration_target(), so how did 
you observe that there are still attempts to isolate such non-suitable 
free large folios? Please explain your usecase in detail.

> Signed-off-by: Wenchao Hao <haowenchao22@...il.com>
> ---
>   mm/compaction.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 3925cb61dbb8..b0ed0831c400 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -656,6 +656,17 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>   
>   		/* Found a free page, will break it into order-0 pages */
>   		order = buddy_order(page);
> +
> +		/*
> +		 * Do not break free pages whose order is larger than
> +		 * compact's desired order
> +		 */
> +		if (cc->order != -1 && order >= cc->order) {
> +			blockpfn += (1 << order) - 1;
> +			page += (1 << order) - 1;
> +			goto isolate_fail;
> +		}
> +
>   		isolated = __isolate_free_page(page, order);
>   		if (!isolated)
>   			break;