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SubjectRe: [PATCH -next v2 1/2] mm: compaction: convert to use a folio in isolate_migratepages_block()
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Hi

On 6/19/2023 7:07 PM, Kefeng Wang wrote:
> Directly use a folio instead of page_folio() when page successfully
> isolated (hugepage and movable page) and after folio_get_nontail_page(),
> which removes several calls to compound_head().
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
> v2:
> - update comments and use node_stat_mod_folio, per Matthew Wilcox
> - add missed PageLRU conversion and rebase on next-20230619
>
> mm/compaction.c | 84 ++++++++++++++++++++++++++-----------------------
> 1 file changed, 44 insertions(+), 40 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 6149a2d324be..0334eefe4bfa 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -795,6 +795,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> struct lruvec *lruvec;
> unsigned long flags = 0;
> struct lruvec *locked = NULL;
> + struct folio *folio = NULL;
> struct page *page = NULL, *valid_page = NULL;
> struct address_space *mapping;
> unsigned long start_pfn = low_pfn;
> @@ -891,7 +892,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> if (!valid_page && pageblock_aligned(low_pfn)) {
> if (!isolation_suitable(cc, page)) {
> low_pfn = end_pfn;
> - page = NULL;
> + folio = NULL;
> goto isolate_abort;
> }
> valid_page = page;
> @@ -923,7 +924,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> * Hugepage was successfully isolated and placed
> * on the cc->migratepages list.
> */
> - low_pfn += compound_nr(page) - 1;
> + folio = page_folio(page);
> + low_pfn += folio_nr_pages(folio) - 1;
> goto isolate_success_no_list;
> }
>
> @@ -991,8 +993,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> locked = NULL;
> }
>
> - if (isolate_movable_page(page, mode))
> + if (isolate_movable_page(page, mode)) {
> + folio = page_folio(page);
> goto isolate_success;
> + }
> }
>
> goto isolate_fail;
> @@ -1003,7 +1007,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> * sure the page is not being freed elsewhere -- the
> * page release code relies on it.
> */
> - if (unlikely(!get_page_unless_zero(page)))
> + folio = folio_get_nontail_page(page);

I'm just curious, how can you make sure the 'page' is not a tail page?
Since the validation is lockless.

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