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

Baolin Wang
2025-04-25T06:53:36Z

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@gmail.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;