linux-kernel - Re: [PATCH v2 1/2] mm: clear pte for folios that are zero filled

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Message-ID: <Zl8GDlOSh56VgRtj@casper.infradead.org>
Date: Tue, 4 Jun 2024 13:18:22 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Usama Arif <usamaarif642@...il.com>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, yosryahmed@...gle.com,
	nphamcs@...il.com, chengming.zhou@...ux.dev, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v2 1/2] mm: clear pte for folios that are zero filled

On Tue, Jun 04, 2024 at 11:58:24AM +0100, Usama Arif wrote:
> +++ b/mm/rmap.c
> @@ -1819,96 +1819,101 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>  			 */
>  			dec_mm_counter(mm, mm_counter(folio));
>  		} else if (folio_test_anon(folio)) {
> -			swp_entry_t entry = page_swap_entry(subpage);
> -			pte_t swp_pte;
> -			/*
> -			 * Store the swap location in the pte.
> -			 * See handle_pte_fault() ...
> -			 */
> -			if (unlikely(folio_test_swapbacked(folio) !=
> -					folio_test_swapcache(folio))) {
> +			if (flags & TTU_ZERO_FOLIO) {
> +				pte_clear(mm, address, pvmw.pte);
> +				dec_mm_counter(mm, MM_ANONPAGES);
> +			} else {

This is very hard to review.  Is what you've done the same as:

			if (flags & TTU_ZERO_FOLIO) {
				pte_clear(mm, address, pvmw.pte);
				dec_mm_counter(mm, MM_ANONPAGES);
				goto discard;
			}

?  I genuinely can't tell.