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t=1793175711; bh=JbQ39/f3ASQKleDrdvaHaj6KcDl8Bzg/BJL2F5+HWZw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=lo8yN/ZD7PTJAuyTezKHOR1S2XSvFaPwIb+JSQUm7CJIGxtgbBqO9ScRWAfTIZAdJ 0y1HZBF3TwjbMrS2/R45EENexfZ2zgb8NgBkBGAnFPq6p/o2Bmy+HxMQ0J9OHdVPRx GvNrAzuywX5nT7wZ5ADy95kzFEf/4k+DFDbkKkyMptMgj2k8qA1uN+yjzn+k68K0R+ cB1bSScHHNP5Ur7Ryx8UMSjpNpUN2j3pr4UOVUsJOoBIdfw629npgMXIO7As1vNdQ5 cH3i8rnIBSFO/suQ9NBdtcGN6BD2jKVcb8ghtfeko/D6TrFZ3x9ZUfliUF5N/v+hKO 35+OqUKYsgaEA== Message-ID: <10ae2533-cc4b-4c30-95d7-705815ba7830@kernel.org> Date: Wed, 28 Oct 2026 09:21:41 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 12/14] mm/shmem: fix truncate loop after boundary swapin failure To: Baolin Wang , Andrew Morton , Gregory Price , Zi Yan , Joshua Hahn , Rakie Kim , Ying Huang , Johannes Weiner , Vladimir Davydov , Michal Hocko , Hugh Dickins , Lukas Czerner , Carlos Maiolino , Christian Brauner , Jan Kara , Daniel Verkamp , Jeff Xu , Muchun Song , Oscar Salvador , David Stevens , "Matthew Wilcox (Oracle)" , William Kucharski , Chris Li , Kairui Song , Nhat Pham , Miaohe Lin , Naoya Horiguchi Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, "Kiryl Shutsemau (Meta)" References: <20261027-fixes_shmem-v2-0-86a00952acb9@kernel.org> <20261027-fixes_shmem-v2-12-86a00952acb9@kernel.org> <2d111275-e7a8-4ac5-8618-f068e87145f2@linux.alibaba.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 5crxysgs6q8551okotztcryrxbcdc65x X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D375840004 X-Rspam-User: X-HE-Tag: 1793175712-694154 X-HE-Meta: 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 B85vD6zb rrJqmERVj0a9VW+0PscOjUMnzpMMRbAUArSHp0vV2nm88+HLZVvxIh3mt3tYjd/pCAVLqSe02t7OihwwjhXipPckdHC1ZrXgIuL0Mnma5jCKgJv9tsujNdfHBMAd1h4fMwBDdFM3u2paZ6ERI6pY/v71bJb9sqOZxR5LkglVyC4VIShWQWbTvldvbkFyOdJ0a2x0xH5vF+vEg73yYj6nQd/jI+MadX/nznB1oKPgeDqCfZKy8aYVLC60LMP0ZON/CezNDHMfS5NIY8WjmoV8sqODZDYuuqWeN2GndmSZ+9kTObhtX/pPloU/bW+tj9LN4NGMw4/k80Hg5QjwZlXrmcrlVeQ== 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 02:30, Baolin Wang wrote: > > > On 10/27/26 9:03 PM, David Hildenbrand (Arm) wrote: >> If swapping in a large entry at the new EOF fails, shmem_undo_range() >> leaves the entry in place. Its final scan skips the entry, then restarts >> from the same start index and finds it again. Truncation can loop forever >> while holding i_rwsem. > > Right. But ... > >> Advance start past the skipped entry so that a restarted scan can finish, >> as we already do for folios that cannot be split. > > IIRC, we originally avoided advancing start because a concurrent swapin fault > could split the boundary large swap entry via shmem_split_large_entry(), leaving > small swap entries below the new start. > > Sigh. > > There doesn't seem to be a simple fix. We may need to swap in the large entry as > shmem_get_partial_folio() does, and then split the large folio. I'll work on > this as a follow-up. Thanks! So you are fine with the patch as is to fix the endless loop? -- Cheers, David