Re: [PATCH 2/4] mm: compaction: convert to folio_isolate_movable()

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Hi Kefeng,

On 2024/8/26 12:01, Kefeng Wang wrote:
> The tail page will always fail to isolate for non-lru-movable and
> LRU page in isolate_migratepages_block(), so move PageTail check
> ahead, then convert to use folio_isolate_movable() helper and more
> folios.
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>   mm/compaction.c | 32 +++++++++++++++++---------------
>   1 file changed, 17 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a2b16b08cbbf..aa2e8bb9fa58 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1074,39 +1074,41 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>   			}
>   		}
>   
> +		if (PageTail(page))
> +			goto isolate_fail;
> +
> +		folio = page_folio(page);

I wonder if this is stable. Before page_folio(), it does not hold a 
reference on the page, so seems we should re-check the folio still 
contains this page after gaining a reference on the folio?

>   		/*
>   		 * Check may be lockless but that's ok as we recheck later.
> -		 * It's possible to migrate LRU and non-lru movable pages.
> -		 * Skip any other type of page
> +		 * It's possible to migrate LRU and non-lru movable folioss.
> +		 * Skip any other type of folios.
>   		 */
> -		if (!PageLRU(page)) {
> +		if (!folio_test_lru(folio)) {
>   			/*
> -			 * __PageMovable can return false positive so we need
> -			 * to verify it under page_lock.
> +			 * __folio_test_movable can return false positive so
> +			 * we need to verify it under page_lock.
>   			 */
> -			if (unlikely(__PageMovable(page)) &&
> -					!PageIsolated(page)) {
> +			if (unlikely(__folio_test_movable(folio)) &&
> +					!folio_test_isolated(folio)) {
>   				if (locked) {
>   					unlock_page_lruvec_irqrestore(locked, flags);
>   					locked = NULL;
>   				}
>   
> -				if (isolate_movable_page(page, mode)) {
> -					folio = page_folio(page);
> +				if (folio_isolate_movable(folio, mode))
>   					goto isolate_success;
> -				}
>   			}
>   
>   			goto isolate_fail;
>   		}
>   
>   		/*
> -		 * Be careful not to clear PageLRU until after we're
> -		 * sure the page is not being freed elsewhere -- the
> -		 * page release code relies on it.
> +		 * Be careful not to clear lru flag until after we're
> +		 * sure the folio is not being freed elsewhere -- the
> +		 * folio release code relies on it.
>   		 */
> -		folio = folio_get_nontail_page(page);
> -		if (unlikely(!folio))
> +		if (unlikely(folio_try_get(folio)))
>   			goto isolate_fail;
>   
>   		/*