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Received: from willy by casper.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1weh27-00000005cZQ-1Zuh; Tue, 30 Jun 2026 22:34:23 +0000 Date: Tue, 30 Jun 2026 23:34:23 +0100 From: Matthew Wilcox To: Pedro Falcato 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-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 5F4CA1C0004 X-Stat-Signature: aakbt74or1po4dqpxh77cps6occdmft1 X-HE-Tag: 1782858867-412895 X-HE-Meta: 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 /F18+9oW 3g8OlePnpU+uR3vOoW1eZw2EUZljH+iTDrJ8yO8aYw00xY0bz2QJC3ZslPH0eU9iBTiqcEtUxNQwfVGl8HQAG85dobafQQC0TE4JETok2xMIu1L0eOCUfCWiHRjXoaNhKS0qBDWQcmT9iAw8k41guMfJbScHzw9ijgpCRfPQNacQhbktq1hZLG0fnATUziwW7WPXblPbZIBS9aCLbf1tgYS0v2LeITE8s5oYf0i/D9+sLAe4eJ5m+ruiF/6COr4llR/VjSyKnzeQbxd6/wiaUcqRG9Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 30, 2026 at 08:55:12PM +0100, Pedro Falcato wrote: > Gregg, if you could test this patch, it would be much appreciated. This patch > (hopefully) makes it so no dirty folio will ever coexist with a ro-THP, thus > hopefully sidestepping the entire issue in a simple way. Only compile-tested > and not reviewed. I'd suggest this is slightly misplaced; it's actually called in some failure places (eg: if (!folio_isolate_lru(folio)) { result = SCAN_DEL_PAGE_LRU; goto out_unlock; ... out_unlock: folio_unlock(folio); folio_put(folio); goto xa_unlocked; ... xa_unlocked: try_to_unmap_flush(); I'd expect to see your new code inside the existing 'if (!is_shmem) {' block immediately before the xa_locked label. I'd also follow the inode_is_open_for_write() case and decrement nr_thps there rather than introducing a new SCAN code. > -- > Pedro > >From 43d90a937f0b24656a8d0405035c3efcfdf0961e Mon Sep 17 00:00:00 2001 > From: Pedro Falcato > Date: Tue, 30 Jun 2026 20:48:41 +0100 > Subject: [PATCH] mm/khugepaged: write all dirty folios when collapsing > > Signed-off-by: Pedro Falcato > --- > mm/khugepaged.c | 19 ++++++++++++++++--- > 1 file changed, 16 insertions(+), 3 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index a97b20617869..3f0f90ab16ba 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -60,6 +60,7 @@ enum scan_result { > SCAN_STORE_FAILED, > SCAN_COPY_MC, > SCAN_PAGE_FILLED, > + SCAN_WRITEBACK_FAIL, > }; > > #define CREATE_TRACE_POINTS > @@ -1812,7 +1813,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, > pgoff_t index = 0, end = start + HPAGE_PMD_NR; > LIST_HEAD(pagelist); > XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER); > - int nr_none = 0, result = SCAN_SUCCEED; > + int nr_none = 0, result = SCAN_SUCCEED, err; > bool is_shmem = shmem_file(file); > > VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); > @@ -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; > + } > + > if (result == SCAN_SUCCEED && nr_none && > !shmem_charge(mapping->host, nr_none)) > result = SCAN_FAIL; > @@ -2210,9 +2222,10 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, > /* > * Undo the updates of filemap_nr_thps_inc for non-SHMEM > * file only. This undo is not needed unless failure is > - * due to SCAN_COPY_MC. > + * due to SCAN_COPY_MC or SCAN_WRITEBACK_FAIL. > */ > - if (!is_shmem && result == SCAN_COPY_MC) { > + if (!is_shmem && (result == SCAN_COPY_MC || > + result == SCAN_WRITEBACK_FAIL)) { > filemap_nr_thps_dec(mapping); > /* > * Paired with the fence in do_dentry_open() -> get_write_access() > -- > 2.55.0 >