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[2003:cb:c72e:800:d383:9661:5934:2cfa]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-436e2e92794sm54178075e9.37.2025.01.09.05.05.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Jan 2025 05:05:45 -0800 (PST) Message-ID: <4e52d67c-e968-4cf6-9c9b-88646f0d3a23@redhat.com> Date: Thu, 9 Jan 2025 14:05:43 +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> <618798d5-71b2-43d6-8f5c-78d911c5dd43@redhat.com> <20250109083527-e3c77b5f-14f5-467b-9cee-f71c75b2d654@linutronix.de> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 0749240003 X-Stat-Signature: h1976jgxsuwk87t16aray68rgefrhqwe X-Rspam-User: X-HE-Tag: 1736427949-672310 X-HE-Meta: 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 +KWS+QKC ZSMU1nDo+Ka/F2FKIA+z8iAlmw3WALBerkX35Lyhusz/HfBHxPD1l9h76seZ8+RGmmWkEcNJR53zSm5U3BLshOlJ5wC4TQzThccgptQiPNHnqujbs4mQ5NcWczQWckLHtlBwjoLY1n0HpwyDGCXQHiq51A/D+4mw6OrDdCINWFGASVF9TZpMtQbwJUy8G7eomYVpJlIQorZKBI5oihm7CxCD7EtjTiVHh/Hjd5lmSVzr0I2K4IvgrICV1ZHtDH9cRqIR+mAKqs16d1UdqkyZqsTCwLizFM8UgPCVdW0E/bOn44lLvyML4GUyHkf2mZJqUG6Z8UsOzTaftBS8gD7LJLrpvY44Y2nj+pqk+cH2+lJQChvSK2IWXSVzWENv0WUm3r5BtglX/PXjWik8HL14ktUX2MqKvCl93Q9n/CHPXS/LSDogurDGm/zX9XH5DCpsqU9tg 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: > > That is clear. The issue would be to figure which chunks are valid to > unmap. If something critical like the executable file is unmapped, > the process crashes. But see below. Ah, now I see what you mean. Yes, also the stack etc. will be problematic. So IIUC, you want to limit the munmap optimization only to the manually mmap()ed parts. > >>> 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? > > First set the VMA name after mmap(): > > for (i = 0; i < NR_CHUNKS_LOW; i++) { > ptr[i] = mmap(NULL, MAP_CHUNK_SIZE, PROT_READ | PROT_WRITE, > MAP_NORESERVE | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > > if (ptr[i] == MAP_FAILED) { > if (validate_lower_address_hint()) > ksft_exit_fail_msg("mmap unexpectedly succeeded with hint\n"); > break; > } > > validate_addr(ptr[i], 0); > if (prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ptr[i], MAP_CHUNK_SIZE, "virtual_address_range")) > ksft_exit_fail_msg("prctl(PR_SET_VMA_ANON_NAME) failed: %s\n", strerror(errno)); Likely this would prevent merging of VMAs. With a 1 GiB chunk size, and NR_CHUNKS_LOW == 128TiB, you'd already require 128k VMAs. The default limit is frequently 64k. We could just scan the ptr / hptr array to see if this is a manual mmap area or not. If this takes too long, one could sort the arrays by address and perform a binary search. Not the most efficient way of doing it, but maybe good enough for this test? Alternatively, store the pointer in a xarray-like tree instead of two arrays. Requires a bit more memory ... and we'd have to find a simple implementation we could just reuse in this test. So maybe there is a simpler way to get it done. -- Cheers, David / dhildenb