Re: [PATCH v1 07/11] mm/huge_memory: convert split_huge_pages_pid() from follow_page() to folio_walk

Pankaj Raghav
2024-08-15T10:04:33Z

Hi David,

On Fri, Aug 02, 2024 at 05:55:20PM +0200, David Hildenbrand wrote:
> continue;
> }
>
> - /* FOLL_DUMP to ignore special (like zero) pages */
> - page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
> -
> - if (IS_ERR_OR_NULL(page))
> + folio = folio_walk_start(&fw, vma, addr, 0);
> + if (!folio)
> continue;
>
> - folio = page_folio(page);
> if (!is_transparent_hugepage(folio))
> goto next;
>
> @@ -3544,13 +3542,19 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
>
> if (!folio_trylock(folio))
> goto next;
> + folio_get(folio);

Shouldn't we lock the folio after we increase the refcount on the folio?
i.e we do folio_get() first and then folio_trylock()?

That is how it was done before (through follow_page) and this patch changes
that. Maybe it doesn't matter? To me increasing the refcount and then
locking sounds more logical but I do see this ordering getting mixed all
over the kernel.

> + folio_walk_end(&fw, vma);
>
> if (!split_folio_to_order(folio, new_order))
> split++;
>
> folio_unlock(folio);
> -next:
> folio_put(folio);
> +
> + cond_resched();
> + continue;
> +next:
> + folio_walk_end(&fw, vma);
> cond_resched();
> }
> mmap_read_unlock(mm);
> --
> 2.45.2

--
Pankaj Raghav