Re: [PATCH v6 05/11] mm: split a folio in minimum folio order chunks

From: Matthew Wilcox
Date: Mon Jun 03 2024 - 08:37:04 EST


On Wed, May 29, 2024 at 03:45:03PM +0200, Pankaj Raghav (Samsung) wrote:
> @@ -3572,14 +3600,19 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
>
> for (index = off_start; index < off_end; index += nr_pages) {
> struct folio *folio = filemap_get_folio(mapping, index);
> + unsigned int min_order, target_order = new_order;
>
> nr_pages = 1;
> if (IS_ERR(folio))
> continue;
>
> - if (!folio_test_large(folio))
> + if (!folio->mapping || !folio_test_large(folio))
> goto next;

This check is useless. folio->mapping is set to NULL on truncate,
but you haven't done anything to prevent truncate yet. That happens
later when you lock the folio.

> + min_order = mapping_min_folio_order(mapping);

You should hoist this out of the loop.

> + if (new_order < min_order)
> + target_order = min_order;
> +
> total++;
> nr_pages = folio_nr_pages(folio);
>
> @@ -3589,7 +3622,18 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
> if (!folio_trylock(folio))
> goto next;
>
> - if (!split_folio_to_order(folio, new_order))
> + if (!folio_test_anon(folio)) {

Please explain how a folio _in a file_ can be anon?

> + unsigned int min_order;
> +
> + if (!folio->mapping)
> + goto next;
> +
> + min_order = mapping_min_folio_order(folio->mapping);
> + if (new_order < target_order)
> + target_order = min_order;

Why is this being repeated?

> + }
> +
> + if (!split_folio_to_order(folio, target_order))
> split++;
>
> folio_unlock(folio);
> --
> 2.34.1
>