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Received: from 30.74.144.137(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XDfWWsR_1793156553 cluster:ay36) by smtp.aliyun-inc.com; Wed, 28 Oct 2026 11:02:33 +0800 Message-ID: <4d32bebe-1a00-475c-8320-b303693603fd@linux.alibaba.com> Date: Wed, 28 Oct 2026 11:02:32 +0800 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] shmem: skip empty unmap ranges when punching holes To: Hungyu Lin , hughd@google.com Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261027171753.1485-1-dennylin0707@gmail.com> From: Baolin Wang In-Reply-To: <20261027171753.1485-1-dennylin0707@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 9AA2FC0003 X-Stat-Signature: ebfs433ijy6nn68cy4oio657b6inhmsu X-Spam-Status: No, score=-19.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1793156557-837325 X-HE-Meta: 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 RdrPORDu mD17gvJRT3N/dLqg09hWpr6OGtFr2ev8sKPeew2dcOPdy+WFVPSL26RJAq/8lA+vTZrblo1FAv91v7nHCihHt1sXsysNgvE+SQMGwhiOmfMKcksAr9r6OdAxgGj7fL4oIVu4wCrkwhI7RYHUqfg8oci+J3xX7f8NzIiEpMf9Y2FGy1paUg8qWWLnD0m7r2G8+eHxetqyOGoAN5BcU0q4nXHlA2om1DQo1xoEaDkR1bP9aAw6LccMjbnBkfz3TsmB80j5oBOk91vu62pKvQKP1Oymh2bS/66DgfBVJa9JsEcrXEs8MeNOTA4rtMj7eYvxGE3Y4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/28/26 1:17 AM, Hungyu Lin wrote: > When a hole ends within the first page, shmem_fallocate() calculates > unmap_end as -1. Casting it to u64 makes the range check succeed even > though the hole contains no complete pages. > > For example, punching one byte at offset zero calls unmap_mapping_range() > with a zero length, which means unmap to the end of the file. The file > contents are preserved outside the hole, but unrelated mappings are > removed and must fault back in. This can be reproduced with fallocate -p > -o 0 -l 1 on a mapped tmpfs file. > > Compare the exclusive rounded end against the rounded start to skip > empty ranges. Keep the unsigned comparison so rounding the start near > the maximum file offset continues to be handled correctly. > > Fixes: 83e4fa9c16e4 ("tmpfs: support fallocate FALLOC_FL_PUNCH_HOLE") > Signed-off-by: Hungyu Lin > --- LGTM. Reviewed-by: Baolin Wang