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Wed, 23 Sep 2026 06:30:17 -0700 (PDT) Received: from [100.125.248.95] ([124.70.231.46]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8a466ab7e7csm9385007b3.44.2026.09.23.06.29.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Sep 2026 06:30:16 -0700 (PDT) Message-ID: <5419d3e7-bd3e-40a5-a15d-397e9019b3d5@gmail.com> Date: Wed, 23 Sep 2026 21:29:56 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 4/4] mm/truncate: clarify return value of truncate_inode_partial_folio() To: Jan Kara , 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, ziy@nvidia.com, 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: <20260922110703.468389-1-yi.zhang@huaweicloud.com> <20260922110703.468389-5-yi.zhang@huaweicloud.com> <5pthbyxtn7q6xi4fmkofvksmcjzfnujcw2g4fxmxjzfin5pbgf@zui3vcimb4cv> Content-Language: en-US From: Zhang Yi In-Reply-To: <5pthbyxtn7q6xi4fmkofvksmcjzfnujcw2g4fxmxjzfin5pbgf@zui3vcimb4cv> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: rhouq6quj9594zhd94nkuu879edzxgej X-Rspamd-Queue-Id: 699B72000A X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1790170218-993713 X-HE-Meta: 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 jou0LtxX 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/22/2026 7:58 PM, Jan Kara wrote: > On Tue 22-09-26 19:07:03, Zhang Yi wrote: >> From: Zhang Yi >> >> With the earlier rework the callers no longer rely on the return value >> of truncate_inode_partial_folio() to decide whether to adjust the >> truncation range. The pstart/pend out-parameters carry that information >> instead. The callers now only use the return value as a flag indicating >> whether the loop should be reset to pick up newly split sub-folios on >> the shmem path. >> >> Return true if at least one split succeeded, and false otherwise. >> This clarifies the existing confusing return value semantics. >> >> Signed-off-by: Zhang Yi > > Looks good to me. Feel free to add: > > Reviewed-by: Jan Kara > > Just as I'm checking the only use of the return value of > truncate_inode_partial_folio() in shmem_undo_range(), the code there looks > fishy. It does: > > } else if (truncate_inode_partial_folio(folio, lstart, lend)) { > /* > * If we split a page, reset the loop so > * that we pick up the new sub pages. > * Otherwise the THP was entirely > * dropped or the target range was > * zeroed, so just continue the loop as > * is. > */ > if (!folio_test_large(folio)) { > folio_unlock(folio); > index = start; > break; > } > } > > However if folio was say order-2 (4 pages), lstart is inside the 3rd page, > then the split done by truncate_inode_partial_folio() can result in order-1 > folio, and two order-0 folios. Hence the !folio_test_large(folio) check > fails and we won't pickup the new smaller folios so that we can free the > 4th one... So I think we need to unconditionally reset the loop if > truncate_inode_partial_folio() returned true. > > Honza Indeed, that's a good point. Since this is a pre-existing and independent issue, I'll send a separate patch to fix it. Thanks, Yi.