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	Wed, 01 Jul 2026 11:54:52 +0000
Date: Wed, 1 Jul 2026 12:54:52 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Pedro Falcato <pfalcato@suse.de>
Cc: Gregg Leventhal <gleventhal@janestreet.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Song Liu <song@kernel.org>, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Eric Hagberg <ehagberg@janestreet.com>,
	David Hildenbrand <david@kernel.org>,
	Lorenzo Stoakes <ljs@kernel.org>, Zi Yan <ziy@nvidia.com>
Subject: Re: Subject: [BUG/RFC] write-open file THP cache purge can discard
 dirty page cache
Message-ID: <akUADHLWEetveHLp@casper.infradead.org>
References: <CAFN_u7H_0ECF3jixP=T=U7AH5=Q3wQNvJMo8an3VqUDMerQfUw@mail.gmail.com>
 <akQIIav_zaK6RmIC@pedro-suse.lan>
 <akQO8JtTxmp89GS8@pedro-suse.lan>
 <akQekZUyoKadiGCH@pedro-suse.lan>
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In-Reply-To: <akQekZUyoKadiGCH@pedro-suse.lan>

On Tue, Jun 30, 2026 at 08:55:12PM +0100, Pedro Falcato wrote:
> @@ -2043,6 +2044,17 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
>  	 */
>  	try_to_unmap_flush();
>  
> +	/*
> +	 * If collapse looks to be successful, flush any dirty pages
> +	 * out the page cache. With the nr_thps incremented, there won't be
> +	 * any new writers (nor new dirties).
> +	 */
> +	if (result == SCAN_SUCCEED && !is_shmem) {
> +		err = filemap_write_and_wait(mapping);
> +		if (err)
> +			result = SCAN_WRITEBACK_FAIL;
> +	}

Oh, the other thing is that this should be conditioned on
!mapping_large_folio_support().