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[PATCH v4 1/4] mm/truncate: align truncation boundaries to mapping minimum folio order Cc: , , , , , , , , , , , , , , , , , , , , , , , To: "Zhang Yi" , From: "Zi Yan" X-Mailer: aerc 0.22.0 References: <20260922110703.468389-1-yi.zhang@huaweicloud.com> <20260922110703.468389-2-yi.zhang@huaweicloud.com> In-Reply-To: <20260922110703.468389-2-yi.zhang@huaweicloud.com> X-ClientProxiedBy: BN1PR12CA0024.namprd12.prod.outlook.com (2603:10b6:408:e1::29) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|PH7PR12MB6935:EE_ X-MS-Office365-Filtering-Correlation-Id: bc1e9e98-2931-423b-ea03-08df18be454d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|23010399003|7416014|376014|1800799024|56012099006|6133799003|10067099003|11063799006|4143699003|18002099003|22082099003; X-Microsoft-Antispam-Message-Info: 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kdonoyo5xzne3u811efsnw19uizxnupk X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 8BDB78000F X-HE-Tag: 1790090964-746981 X-HE-Meta: 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 do+otzMf 2nAtVP6b3z9qFJx2kmR/OsXMNHLH/SxUkyhwQrru/SJAtde5AKGMyRQ6moXeufXBW1tnv3C9k3CQm4ALZGBm5F7w/+2mUlus0zHpkUAK7v1LmrTFDBnc7yAqd4o24Km45TMxfzzl8gWMCUN3Lx3p5BMSCOYUcfBD5/au69NuIfltd/3NbcdxDDw8qWp4jP/Kpj/YDVGN5WDT5s3E/MTl2+8UU7L1FBIhYbjl6j6pVIwD7TfLzX5N8eDmfR5Lcow9CCjGftLbQiNIL+D3zUTPqc/efrV4R4fGt5Ey1LfecWof4XyH3uRTyxKJ+B1gb0g1NqxiGGmOBrp+i40c0bkRl1Lwa7ZLDT8DVvSRpZ9m+GXPiHKHwvi2DqHOGI+qV/sF5fHJG64oUxOb+jStMLp6pVJsh6Ye+8tgVv7IqjDYRFzWULho5OOSh0cS5xG9DxkxAqQmhEQrukh1tlrd43Dd1Ng135g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue Sep 22, 2026 at 7:07 AM EDT, Zhang Yi wrote: > From: Zhang Yi > > When the mapping has a non-zero minimum folio order (min_order), > folio_split() in truncate_inode_partial_folio() stops at min_order > instead of order 0, so the sub-folio containing a split point stays > aligned to 1 << min_order rather than to a single page. The original > boundaries in truncate_inode_pages_range() were based on page > granularity, so either boundary could land inside the min_order chunk at > its edge, and the truncation loop would drop that whole chunk, valid > out-of-range tail included. > > For example, a 64K (order-4) folio with min_order =3D 2 (16K) punched fro= m > offset 0 to 36K: > > split @p0 -> [p0-p3, p4-p7, p8-p15] # non-uniform, min_order > folio2 =3D p8-p15 # straddles: p8 in range, p9-p15 tail valid > 2nd split of folio2 -> [p8-p11, p12-p15] # success > end(old) =3D p9 # BUG: p9 inside [p8-p11] > loop truncates ... p8-p11 # p9-p11's valid tail is lost > > It has gone unnoticed so far for two reasons. A non-zero min_order is > only used by filesystems with a block or sector size larger than the > page size, and those either always write back the affected range before > punching a hole or truncating, or they carry filesystem private data on > dirty folios (e.g. buffer_head), which makes filemap_release_folio() > fail and folio_split() abort with -EBUSY, so the folio is never split > and the old start/end boundaries remain valid. The bug only becomes > reachable on paths that truncate dirty large folios without prior > writeback and without filesystem private data, such as the upcoming ext4 > iomap buffered I/O path. > > Align both start (rounded up) and end (rounded down) to the mapping > minimum folio order so they always fall on a folio boundary. > > Reported-by: Joanne Koong > Link: https://lore.kernel.org/linux-mm/CAJnrk1bQYUe6+1ryyJur5EEnZYrC+_5AY= sy=3DOWzVRgD4202y1g@mail.gmail.com/ > Fixes: e220917fa5077 ("mm: split a folio in minimum folio order chunks") > Suggested-by: Zi Yan > Signed-off-by: Zhang Yi > --- > mm/truncate.c | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) LGTM. Just a nit below. Reviewed-by: Zi Yan > > diff --git a/mm/truncate.c b/mm/truncate.c > index b58ba940be47..f9625bb4916f 100644 > --- a/mm/truncate.c > +++ b/mm/truncate.c > @@ -345,9 +345,11 @@ long mapping_evict_folio(struct address_space *mappi= ng, struct folio *folio) > * @lstart: offset from which to truncate > * @lend: offset to which to truncate (inclusive) > * > - * Truncate the page cache, removing the pages that are between > - * specified offsets (and zeroing out partial pages > - * if lstart or lend + 1 is not page aligned). > + * Truncate the page cache, removing the folios that are between specifi= ed > + * offsets (and zeroing out partial folios if lstart or lend + 1 is not > + * folio aligned). For mappings with a non-zero minimum folio order, th= e > + * boundaries are aligned inwards to 1 << min_order so the edge sub-foli= o > + * straddling the range is kept. > * > * Truncate takes two passes - the first pass is nonblocking. It will n= ot > * block on page locks and it will not block on writeback. The second p= ass > @@ -374,14 +376,14 @@ void truncate_inode_pages_range(struct address_spac= e *mapping, > int i; > struct folio *folio; > bool same_folio; > + pgoff_t min_nrpages =3D mapping_min_folio_nrpages(mapping); > =20 It is better to put it at the top (reverse christmas tree). --=20 Best Regards, Yan, Zi