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Fri, 04 Jul 2025 11:27:23 +0800 Message-ID: Date: Fri, 4 Jul 2025 11:27:22 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] khugepaged: Reduce race probability between migration and khugepaged To: Dev Jain , akpm@linux-foundation.org, david@redhat.com Cc: ziy@nvidia.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250703054823.49149-1-dev.jain@arm.com> From: Baolin Wang In-Reply-To: <20250703054823.49149-1-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 04445A000A X-Rspamd-Server: rspam09 X-Stat-Signature: n1ckc5bbmhwmckn6jut38ykps7udrskw X-HE-Tag: 1751599647-999929 X-HE-Meta: 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 AK6l9G5N JlQo/czvW4KMVljjk4qXaeouqTmFaiB3Ih9PJyk7LU7lUzQ9Uhd2VkMzC1cY6JIGl6SfXAkqMbghx+2F+ZEtKB4tGAYW/oQ1MRijihcwfkskEBaL4OIdIPb0BXPbHlknkFVLPXY6dQsUTO3GJMNM2Y1U8IS//+Cpm8Gv2Doc8FYrcR3OMnfKxWY1LESwq23Cr24KVYPMLuXTFVMXNM1dyWCaxszUZp7CtjizCunaGoE8MopqQzcVE/bZyCBUOuQMQTOBod8+Iugn7n621Oivz7SK3wLctsv3mHqP/Fo/ZGN7/nb4EFsiFUzMoXTMdsxH6LMslW41GT70JxhY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025/7/3 13:48, Dev Jain wrote: > Suppose a folio is under migration, and khugepaged is also trying to > collapse it. collapse_pte_mapped_thp() will retrieve the folio from the > page cache via filemap_lock_folio(), thus taking a reference on the folio > and sleeping on the folio lock, since the lock is held by the migration > path. Migration will then fail in > __folio_migrate_mapping -> folio_ref_freeze. Reduce the probability of > such a race happening (leading to migration failure) by bailing out > if we detect a PMD is marked with a migration entry. > > This fixes the migration-shared-anon-thp testcase failure on Apple M3. > > Note that, this is not a "fix" since it only reduces the chance of > interference of khugepaged with migration, wherein both the kernel > functionalities are deemed "best-effort". > > Signed-off-by: Dev Jain With David's comments addressed, LGTM. Reviewed-by: Baolin Wang