Re: [RFC 2/2] migrate: convert migrate_pages() to use folios

[Matthew Wilcox <willy@infradead.org>]

On Tue, Nov 01, 2022 at 02:21:37PM +0800, Huang Ying wrote:
> -			is_thp = PageTransHuge(page) && !PageHuge(page);
> -			nr_subpages = compound_nr(page);
> +			is_large = folio_test_large(folio) && !PageHuge(&folio->page);

We have folio_test_hugetlb() to replace PageHuge().

>  	count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
>  	count_vm_events(PGMIGRATE_FAIL, nr_failed_pages);
> -	count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);
> -	count_vm_events(THP_MIGRATION_FAIL, nr_thp_failed);
> -	count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split);
> -	trace_mm_migrate_pages(nr_succeeded, nr_failed_pages, nr_thp_succeeded,
> -			       nr_thp_failed, nr_thp_split, mode, reason);
> +	count_vm_events(THP_MIGRATION_SUCCESS, nr_large_succeeded);
> +	count_vm_events(THP_MIGRATION_FAIL, nr_large_failed);
> +	count_vm_events(THP_MIGRATION_SPLIT, nr_split);
> +	trace_mm_migrate_pages(nr_succeeded, nr_failed_pages, nr_large_succeeded,
> +			       nr_large_failed, nr_split, mode, reason);

I think this is the biggest question with this patch -- how (or whether)
to account folios in size between PMD and PTE size.  Since it's
_called_ THP, I've tended to make the statistics conditional on
folio_test_pmd_mappable() rather than simply being folio_test_large().