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Wed, 1 Jul 2026 12:48:23 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id ohXhE5cMRWqYXgAAD6G6ig (envelope-from ); Wed, 01 Jul 2026 12:48:23 +0000 Date: Wed, 1 Jul 2026 13:48:21 +0100 From: Pedro Falcato To: Matthew Wilcox Cc: Gregg Leventhal , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , Song Liu , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Hagberg , David Hildenbrand , Lorenzo Stoakes , Zi Yan Subject: Re: Subject: [BUG/RFC] write-open file THP cache purge can discard dirty page cache Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 6x13puce88o7p8iumu8smu9fn5cfrk3y X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A571680003 X-HE-Tag: 1782910105-260571 X-HE-Meta: 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 kpM/BRJ2 +u6jR3EUag6Spjfz/oTGG1V53xC9E2TwUCostLodVOs1YBp8jx1XJ7CccsY90Bp+IF48y6AhIYsByaK9spT5XPsPruuu0W8MXDr7agfIX3uAR0zybe9/sC5PmGtYfAWC0y8PaeGcsRanIjUbkiBICjay8XG6h0csWqNZDmWl+1HEE2WTlRC4y7qo3sKITdxR17DJWX+oK6pDNq3PQGBFRRhg+/yqhiaiJKf3AaenzmNUaDX0wgReoh4FZfHSQqsXBcjW/pcdZpZlt29cviBcAZPXxxOeU1ULTOtk8AEdUsWlpChF7BcCC+0C4JQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 01, 2026 at 12:54:52PM +0100, Matthew Wilcox wrote: > 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(). Thinking more about this, I don't think it works. On the file open side, we always truncate the full page cache, even if large folios are supported (due to possibly max folio < PMD_ORDER). So if we skip write-and-wait on such cases, it will be possible to fully reproduce this issue. -- Pedro