linux-kernel - Re: [PATCH v2] mm: Fix for negative counter: nr_file

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Message-ID: <ZUqRia1Ww0+wNfKr@casper.infradead.org>
Date:   Tue, 7 Nov 2023 19:35:37 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Stefan Roesch <shr@...kernel.io>
Cc:     kernel-team@...com, akpm@...ux-foundation.org, hannes@...xchg.org,
        riel@...riel.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] mm: Fix for negative counter: nr_file_hugepages

On Tue, Nov 07, 2023 at 10:18:05AM -0800, Stefan Roesch wrote:
> +++ b/mm/huge_memory.c
> @@ -2740,7 +2740,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>  			if (folio_test_swapbacked(folio)) {
>  				__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
>  							-nr);
> -			} else {
> +			} else if (folio_test_pmd_mappable(folio)) {
>  				__lruvec_stat_mod_folio(folio, NR_FILE_THPS,
>  							-nr);
>  				filemap_nr_thps_dec(mapping);

As I said, we also need the folio_test_pmd_mappable() for swapbacked.
Not because there's currently a problem, but because we don't leave
landmines for other people to trip over in future!