Re: [PATCH] mm: shmem: convert to use folio_zero_range()

[Matthew Wilcox <willy@infradead.org>]

On Thu, Oct 17, 2024 at 10:25:04PM +0800, Kefeng Wang wrote:
> Directly use folio_zero_range() to cleanup code.

Are you sure there's no performance regression introduced by this?
clear_highpage() is often optimised in ways that we can't optimise for
a plain memset().  On the other hand, if the folio is large, maybe a
modern CPU will be able to do better than clear-one-page-at-a-time.

IOW, what performance testing have you done with this patch?

>  	if (sgp != SGP_WRITE && !folio_test_uptodate(folio)) {
> -		long i, n = folio_nr_pages(folio);
> -
> -		for (i = 0; i < n; i++)
> -			clear_highpage(folio_page(folio, i));
> -		flush_dcache_folio(folio);
> +		folio_zero_range(folio, 0, folio_size(folio));
>  		folio_mark_uptodate(folio);
>  	}