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[2003:cb:c70d:3a00:d73c:6a8:ca9f:1df7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-436e2da79c0sm26729805e9.6.2025.01.08.08.46.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Jan 2025 08:46:39 -0800 (PST) Message-ID: <618798d5-71b2-43d6-8f5c-78d911c5dd43@redhat.com> Date: Wed, 8 Jan 2025 17:46:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] selftests/mm: virtual_address_range: Fix error when CommitLimit < 1GiB To: =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= Cc: Dev Jain , Andrew Morton , Shuah Khan , Thomas Gleixner , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Ryan Roberts References: <20250107-virtual_address_range-tests-v1-0-3834a2fb47fe@linutronix.de> <20250107-virtual_address_range-tests-v1-1-3834a2fb47fe@linutronix.de> <5811cf74-d333-4653-ab64-0e981eda7745@arm.com> <20250108083855-840c688b-003f-423b-8327-2a10a2b27d58@linutronix.de> <05edee1e-04f1-4f19-816f-db03c182a201@redhat.com> <20250108165052-c03470bd-6ff7-44c9-87b9-9145456bdea8@linutronix.de> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: a7nffw1gnqrkh15cnit5rwr7iy5zcpzp X-Rspamd-Queue-Id: AC533C000A X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1736354804-21729 X-HE-Meta: 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 88LXNOqX 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 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 08.01.25 17:13, Thomas Weißschuh wrote: > On Wed, Jan 08, 2025 at 02:36:57PM +0100, David Hildenbrand wrote: >> On 08.01.25 09:05, Thomas Weißschuh wrote: >>> On Wed, Jan 08, 2025 at 11:46:19AM +0530, Dev Jain wrote: >>>> >>>> On 07/01/25 8:44 pm, Thomas Weißschuh wrote: >>>>> If not enough physical memory is available the kernel may fail mmap(); >>>>> see __vm_enough_memory() and vm_commit_limit(). >>>>> In that case the logic in validate_complete_va_space() does not make >>>>> sense and will even incorrectly fail. >>>>> Instead skip the test if no mmap() succeeded. >>>>> >>>>> Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()") >>>>> Cc: stable@vger.kernel.org >> >> CC stable on tests is ... odd. > > I thought it was fairly common, but it isn't. > Will drop it. As it's not really a "kernel BUG", it's rather uncommon. >> >> Note that with MAP_NORESRVE, most setups we care about will allow mapping as >> much as you want, but on access OOM will fire. > > Thanks for the hint. > >> So one could require that /proc/sys/vm/overcommit_memory is setup properly >> and use MAP_NORESRVE. > > Isn't the check for lchunks == 0 essentially exactly this? I assume paired with MAP_NORESERVE? Maybe, but it could be better to have something that says "if overcommit_memory is not setup properly I will SKIP this test", but otherwise I expect this to work and will FAIL if it doesn't". Or would you expect to run into lchunks == 0 even if overcommit_memory is setup properly and MAP_NORESERVE is used? (very very low memory that we cannot even create all the VMAs?) > >> Reading from anonymous memory will populate the shared zeropage. To mitigate >> OOM from "too many page tables", one could simply unmap the pieces as they >> are verified (or MAP_FIXED over them, to free page tables). > > The code has to figure out if a verified region was created by mmap(), > otherwise an munmap() could crash the process. > As the entries from /proc/self/maps may have been merged and (I assume) Yes, and partial unmap (in chunk granularity?) would split them again. > the ordering of mappings is not guaranteed, some bespoke logic to establish > the link will be needed. My thinking was that you simply process one /proc/self/maps entry in some chunks. After processing a chunk, you munmap() it. So you would process + munmap in chunks. > > Is it fine to rely on CONFIG_ANON_VMA_NAME? > That would make it much easier to implement. Can you elaborate how you would do it? > > Using MAP_NORESERVE and eager munmap()s, the testcase works nicely even > in very low physical memory conditions. Cool. -- Cheers, David / dhildenb