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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: Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Flag: NO X-Spamd-Result: default: False [-3.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[14]; MISSING_XM_UA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Level: X-Spam-Score: -3.80 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