From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj2-f13.google.com (mail-pj2-f13.google.com [74.125.227.141]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1E9454F30DB for ; Thu, 17 Sep 2026 12:32:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.227.141 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789648385; cv=none; b=UtWmT7gIZFJKSl/lYI6UelfLvLorj1CBoL+JpgmkX7b5L5ke9weid9aRuW5JLBByw5k9u/jlNdEihSpKjUTn10eZOScdj12JojrMkNX8BPdwOS6bElHrOnHPq2thZ5TZZJXDVokM9FDmHbuOZxxPSoUEguTrTX+qEpdCqKZG4cU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789648385; c=relaxed/simple; bh=Xa1IsGUxXNZyPx56uY6l71cj0MjnLhOAqncuS8+Vjcw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=TAHJfOriKQA2tM5pRLL3N1n9Um7qU/E69TDFqWC/Pa2OKEm1vzz0ezeCr6IhTg86YaL69zYWcNzNb80CHH319pCi66DAPTBa544FN7m2sEotpdifnS5c8EtgJkaMdeqeS/zRwiw40VpX/I7k5WBFmpNzlm3CmU7T1t8LbHJJXfg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=hjcXjMtD; arc=none smtp.client-ip=74.125.227.141 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="hjcXjMtD" Received: by mail-pj2-f13.google.com with SMTP id 98e67ed59e1d1-396ccd5cf03so695514a91.1 for ; Thu, 17 Sep 2026 05:32:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1789648365; x=1790253165; darn=vger.kernel.org; h=content-transfer-encoding:content-type:in-reply-to:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:from:to:cc:subject:date:message-id:reply-to :content-type; bh=pX0fdZFc2RLefcqbAqYKYTVdyFNxhnyETiiYgD7pF2c=; b=hjcXjMtDRnxivV5RUwe4t7f8G1xCyCNdN8hpGAmvHPWJPjzqShBjOQDsYzOMLXbYwR xoq4s8fgi0/7l6kzwwbC2PtKx93Znq7uPk3yS9loWfkr9LdBAlnRhtWsLqgRtzAXOV7O EZgvXAV8GwFgE/lMd4pSmhwY0eZmJ4fpWvJpEU9u45btB6rjO0E7KKGYzGOsbHqUcWrM zVHC9aEc6ArGcsq+juf4DIR0TdOU45VQQy1vokAM+tWnXmtMlSCS7Tz2/Asv3WMj7Mti 4+VUMkwLrCu1aNMYTbfVJvthg4BRzFey46NItDsgwlkGQyrb5Xx0r/HjumMIEfsBcjCO Rqjw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789648365; x=1790253165; h=content-transfer-encoding:content-type:in-reply-to:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=pX0fdZFc2RLefcqbAqYKYTVdyFNxhnyETiiYgD7pF2c=; b=DJIBLGkyuZj7wTku2xUyeSYOqvUkROjFfWbSywPATq+aLdBkbBx+YJrHpIjL66v0RU 0mR3iBaSe/AutJnj1FgAtE/0j3cQtqMVxj0Ut8Y+qjnqCNQEEr19kgwZTEBEtUUuyTqJ cm9TobuqpA0mUNLPWQxkHY4brUTxaP0NdqfzuzXmldfGp17gaEVB3w8RabDNgL3+MNL6 wPmWQ+jOlUqKnCsUYlP3LuKSzFRkJ2lHa0cWNK1vTuf4f/fREsgliZ9gtYvv0lw4RaV3 X6fYeYM2qyLYpGRiaHMHgRQgnD3ZYp3RhegfnQxw0Abwx9YwB6xZ98FrYFH3F5fmn0o0 oV/w== X-Forwarded-Encrypted: i=1; AKwUvBxLsMsp6q+/MtE7jnASRo8Ecn80Od40JoCl0Yb3m53mn+nMWP+asj6Jbeo+q/tVcZlQHVQ+xsj/lOjF@vger.kernel.org X-Gm-Message-State: AFuF++nas1pAgO2wt9pTElTN93vhhXOV6vDcyP+glVNF7zxm2+oOvLrZ ktc6SXWbX3TnFbR/+LK2D7N1AwZq3OR4Gs8W2YXdOR/hvFvCP6IGAajJ X-Gm-Gg: AYBFou1aPr4r64M3HA7FqdTuAJw9zNtPSV7ElkJ6qZGl9jkiJVcOmHohky9TMbaCDgh CXrARcVEDEbpDBeqPoITfucp2YavJEi26aovU2NyVIJqtPkn3msbDqolhURvaJmDIaT0jIABAda 2YQa3kCiy1616DrMipov4DPPTLY+WklDZMqKaD2L0fByDOm3QXYmFI22ZC6vFKLbCauRLRoiBTi ofnrdihhR2qlTbhVNqMQ3zwTvLLSxJg5QSY9bBo/kRRsILmn5DFqo2Ke45CpyEFDYfLvPvh9D87 ztGa4MMgC8gOO2x24sQ7Vanlm7gwJE3QcFixGgxPK18bzAoHGIooBaXv/ICMdU/mnQE5WPEDSgn uYNjJNsLo57CZK4u1WzjFXNcUAFPvlp2Tsv3/P9RNKW5TETj9um4nsl2S9gpdKhVxadI0S9Fae+ uNIIb3bvPzRwbEy++3yl307/8NMAbvi4WGYHzk+7c5s5n8O1n4ux7PBrjk9qtLAAKD0lH/pvKdQ nDXfU10hiEKzSEAfUo= X-Received: by 2002:a17:90b:2c86:b0:39e:4c80:f67d with SMTP id 98e67ed59e1d1-39e4c80f73cmr236031a91.28.1789648364901; Thu, 17 Sep 2026 05:32:44 -0700 (PDT) Received: from [100.125.248.95] ([124.70.231.46]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39e35d9869csm5164981a91.4.2026.09.17.05.32.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Sep 2026 05:32:44 -0700 (PDT) Message-ID: <997ebbdf-efc9-4dc2-91ee-254c66176c32@gmail.com> Date: Thu, 17 Sep 2026 20:32:19 +0800 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] mm/truncate: align truncation boundaries to mapping minimum folio order To: Zi Yan , Zhang Yi Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, hughd@google.com, baolin.wang@linux.alibaba.com, willy@infradead.org, jack@suse.cz, bfoster@redhat.com, joannelkoong@gmail.com, djwong@kernel.org, yi.zhang@huawei.com, yangerkun@huawei.com, chengzhihao1@huawei.com, wangkefeng.wang@huawei.com, yukuai@fnnas.com References: <20260916092450.654408-1-yi.zhang@huaweicloud.com> <20260916092450.654408-3-yi.zhang@huaweicloud.com> Content-Language: en-US From: Zhang Yi In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/17/2026 5:14 AM, Zi Yan wrote: > On Wed Sep 16, 2026 at 5:24 AM EDT, Zhang Yi wrote: >> From: Zhang Yi >> >> When the mapping has a non-zero minimum folio order (min_order), >> folio_split() 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 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 = 2 (16K) punched from >> offset 0 to 36K: >> >> split @p0 -> [p0-p3, p4-p7, p8-p15] # non-uniform, min_order >> folio2 = p8-p15 # straddles: p8 in range, p9-p15 tail valid >> 2nd split of folio2 -> [p8-p11, p12-p15] # success >> end(old) = 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+_5AYsy=OWzVRgD4202y1g@mail.gmail.com/ >> Fixes: e220917fa5077 ("mm: split a folio in minimum folio order chunks") >> Signed-off-by: Zhang Yi >> --- >> mm/truncate.c | 14 ++++++++------ >> 1 file changed, 8 insertions(+), 6 deletions(-) >> > > This should be the first patch, since Fixes is older than the one in > patch 1. > > It can adjust start and end in truncate_inode_pages_range() instead, > since shmem's min_order is always 0. > > Something like below. > > Am I missing anything? Thanks. Yeah, this makes sense to me, thanks for your suggestion. Yi. > > diff --git a/mm/truncate.c b/mm/truncate.c > index b58ba940be474..803ee61ebf624 100644 > --- a/mm/truncate.c > +++ b/mm/truncate.c > @@ -374,6 +374,7 @@ void truncate_inode_pages_range(struct address_space *mapping, > int i; > struct folio *folio; > bool same_folio; > + pgoff_t min_nrpages = mapping_min_folio_nrpages(mapping); > > if (mapping_empty(mapping)) > return; > @@ -395,6 +396,10 @@ void truncate_inode_pages_range(struct address_space *mapping, > else > end = (lend + 1) >> PAGE_SHIFT; > > + start = round_up(start, min_nrpages); > + if (end != (pgoff_t)-1) > + end = round_down(end, min_nrpages); > + > folio_batch_init(&fbatch); > index = start; > while (index < end && find_lock_entries(mapping, &index, end - 1, >