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Date:   Mon, 6 Nov 2023 18:59:55 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Stefan Roesch <shr@devkernel.io>
Cc:     kernel-team@fb.com, akpm@linux-foundation.org, hannes@cmpxchg.org,
        riel@surriel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v1] mm: Fix for negative counter: nr_file_hugepages
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On Mon, Nov 06, 2023 at 10:19:18AM -0800, Stefan Roesch wrote:
> +++ b/mm/huge_memory.c
> @@ -2740,7 +2740,8 @@ 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);

Good catch.  Two things:

1. No blank line after the 'else if'.

2. We're leaving a bit of a landmine for shmem when it gets support for
arbitrary folio sizes.  Really all of this should be under a
test_pmd_mappable.