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b=eP4fmrHeRepHJ0pA0bpACG1sSKddJlzxQYKGjO2sPLYRp2GO/6aI2gyHnltcbzz/w f1YKgHF8aG4zSjc384gmDeq8DWygduXo3UGRiJ/1yTYQPnAtOEyf+XSAQb00X8YNHv KosuDzJzDhq4TYM2bYt5FAi1UuatWoGJTk43veDc= Date: Tue, 9 Jan 2024 21:47:31 -0800 From: Andrew Morton To: Breno Leitao Cc: riel@surriel.com, linux-mm@kvack.org, Shuah Khan , vegard.nossum@oracle.com, rppt@kernel.org, songmuchun@bytedance.com, shy828301@gmail.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] selftests/mm: new test that steals pages Message-Id: <20240109214731.a7694ae4a575be838b40e9ea@linux-foundation.org> In-Reply-To: <20240105155419.1939484-2-leitao@debian.org> References: <20240105155419.1939484-1-leitao@debian.org> <20240105155419.1939484-2-leitao@debian.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 43963140018 X-Rspam-User: X-Stat-Signature: gbx9nxpbqeespy88tz1o94z8b5csdadh X-Rspamd-Server: rspam03 X-HE-Tag: 1704865654-761509 X-HE-Meta: U2FsdGVkX1+kpKeO7ZMHt6AkR1rLqbExMRprJ0Nf/lEOPBcJQksozMG9ZmnUNxQt+iid+lUk1fqFWblGUtIZQWbLSvYQIf76qNCaUlibqsMI7DHJlTzj9OodF+wVAlgWR68YE9H3J3X45rnXU6VUqNuCyv0T2XJ5AYWwuUSr29ncLqfX6G6VOJ6UgIWbpCkOLYf0mNk8NKICPgMiHQESC2qO6fIHSXEE8enj0CoVcKeLOnI+K2X8J7UNLZ+JkDKHHWfGkLLogGFB4fxEe/CtUFG0rnRPVh075uJtMLec9SvKERB5ayLxm8g9S6jW9ZMTXrxigoBhBzT7xUKVlERpzCSSi2Pyt8Ipj3o2ymm8rH7Lob5qmRcZefMhvcYzP0NxywkyD+9h3UUaq0S9M8vHobtfGLs0Y8wXU75tjMZ1qBoIQZdoAZAJ8GoluzRW8UtFVDWc80UJmDVj/Iyob/P8PYieMbAPN5TEwCmzHzDccnKT6/xIPcS0XR1tfqzCi0mHArAFHax0RiqZ58D8vJmWMTKYs2sVyHrE4Rrck4IoZ9SwBpYhYXxqDyjBtXkNCX3wAwmaqy3I6SEWEQRudfb5FdrDwkDYT/3zO7cd9aicEgHBBLpuTtQQ4tMlnoSKA/WcjmSkgN4JT9+fg+U2qaLl/HxCWxMhlEPoyahTI2hkbwCUYrazfBIPxMNiay595rU/bhaHx2yHRZHpt7PwG/vwJe6/vWo1Uef1C98bq4LEtxkrpJSjOgXPxJnmaRmG/kXAYEqCLnOFA0IkSGBgQfZMLp7IdtgQltbtaePFde8lbDv8Mgya3ZSsm4MbhiFGs+C3feqZRZ9QuAfXXK42lypmgGwPvz9wYhl9wtktliwfmc0EulqW6eWiyftM5zV4Keh6ALoP6ZEl2GkKsxEm2WdgnSmMuGHZ5Z8PigBSgaj8vWc= 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 Fri, 5 Jan 2024 07:54:19 -0800 Breno Leitao wrote: > This test stresses the race between of madvise(DONTNEED), a page fault > and a parallel huge page mmap, which should fail due to lack of > available page available for mapping. > > This test case must run on a system with one and only one huge page > available. > > # echo 1 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages Can't the test framework perform this configuration prior to running the test? > During setup, the test allocates the only available page, and starts > three threads: > > - thread 1: > * madvise(MADV_DONTNEED) on the allocated huge page > - thread 2: > * Write to the allocated huge page > - thread 3: > * Tries to allocated (steal) an extra huge page (which is not > available) > > thread 3 should never succeed in the allocation, since the only huge > page was never unmapped, and should be reserved. > > Touching the old page after thread3 allocation will raise a SIGBUS. > It's a bit strange to merge a selftest which is expected to fail because of a known but unfixed kernel bug. But I'll toss the test in there anyway, as we deserve to get bug reports ;)