On 1/22/24 14:01, Baolin Wang wrote:
> It can not improve the fragmentation if we isolate the target free pages
> exceeding cc->order, especially when the cc->order is less than pageblock_order.
> For example, suppose the pageblock_order is MAX_ORDER (size is 4M) and cc->order
> is 2M THP size, we should not isolate other 2M free pages to be the migration
> target, which can not improve the fragmentation.
>
> Moreover this is also applicable for large folio compaction.
So why not Cc: Zi Yan? (done)
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
I doubt this will make much difference, because if such a larger order free
page exists, we shouldn't have a reason to be compacting for a lower order
in the first place?
> ---
> mm/compaction.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 27ada42924d5..066b72b3471a 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1346,12 +1346,14 @@ static bool suitable_migration_target(struct compact_control *cc,
> {
> /* If the page is a large free page, then disallow migration */
> if (PageBuddy(page)) {
> + int order = cc->order > 0 ? cc->order : pageblock_order;
> +
> /*
> * We are checking page_order without zone->lock taken. But
> * the only small danger is that we skip a potentially suitable
> * pageblock, so it's not worth to check order for valid range.
> */
> - if (buddy_order_unsafe(page) >= pageblock_order)
> + if (buddy_order_unsafe(page) >= order)
> return false;
> }
>
