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Received: from [2a02:8108:8984:1d00:a0cf:1912:4be:477f]; authenticated by wp530.webpack.hosteurope.de running ExIM with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) id 1vmUid-00EMA7-04; Sun, 01 Feb 2026 11:30:15 +0100 Message-ID: Date: Sun, 1 Feb 2026 11:30:14 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Regression: CONFIG_ASYNC_KERNEL_PGTABLE_FREE causes memory exhaustion and stalls on busy Cascade Lake server (6.18.7 only) To: Robert Dinse , akpm@linux-foundation.org Cc: linux-mm@kvack.org, Linux kernel regressions list , "stable@vger.kernel.org" References: <06843c7a-909b-41e5-9359-2be51cf9dffa@eskimo.com> From: Thorsten Leemhuis Content-Language: de-DE, en-US In-Reply-To: <06843c7a-909b-41e5-9359-2be51cf9dffa@eskimo.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-bounce-key: webpack.hosteurope.de;regressions@leemhuis.info;1769941817;45e25e53; X-HE-SMSGID: 1vmUid-00EMA7-04 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: B25FD140006 X-Stat-Signature: w99yu516zhn6p85kg1xyf5ayhbhm65pp X-Rspam-User: X-HE-Tag: 1769941817-988798 X-HE-Meta: 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 8t8pkTwA VvqIncljp+718ex5HUBrJ0lfkrPzP5py+06IDIaH5BAKR9smkfEvIoCtO0zYs58eX1ZYH2wEloOycoPZQEIVgheR2M2TpGoIPPXT4nwBKb2on6p4X+dBxnOHz07InEs/O4n7kH7KfpSlkTNVfIcsFNYgMed61AhdNAMrjTd+/gum1pqK5RMnQcyOEp7I45O8M5un+9+EuoQZ2ZMVz9GAG2efII2xmdQgwpbSdIIIyzAjQpOUSFWhn4t9j5oQQsWC3vzmnp3jHde5BgyfDtWr5zg9KGMynekDNlo5nVEZo/UdzvRykl6Bx2nfmtKbztpE+ItAYrtTo+Q48CPquQUo3JS+yDXijdcBQOFjCelWQd7KfuFlebqdc/JYxahtQGQl9oukfy7PhnnQyKrE98nXJ2q7aOHjVBlCT2QMj12p5ngHUeZc+6S9D5YRnQC1zQgkThh0otHva3p31doHnnK4D+nwLuFuz5djLQXmWeoHi+isItrc= 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: Lo! Top-posting to facilitate processing and CCing the stable list, maybe someone has heard of a problem. Thx for the report. The big questions here is: Is that something that is specific to 6.18.y or does it happen with mainline, too? And does it still happen with the latest 6.18.y version (there were a few mm fixes)? Without answers to this question nobody might look into this if we are unlucky. And a bisection would be ideal, but I understand all that is not easy if it takes 24h to detect the problem. Ciao, Thorsten On 1/29/26 07:10, Robert Dinse wrote: > > Hardware / setup > ---------------- > - CPU: Intel i9-10980XE (Cascade Lake), all cores overclocked to 4.5 GHz > - Motherboard: Gigabyte Aorus Master X299 > - PSU: 1200W Seasonic > - RAM: 256 GB > - Storage: >   - MariaDB: RAID1 of two 1 TB NVMe drives >   - Other storage: RAID1 arrays of spinning disks > > Software > -------- > - OS: Ubuntu 24.04, with most userland and kernel replaced by self- > compiled upstream > - Kernel: >   - 6.18.6: stable, previously in production >   - 6.18.7: regression > - Toolchain: gcc 15.2 > - Services: >   - Apache 2.4.65 (self-compiled), with modified exec-php to allow per- > user PHP versions via handlers >   - MariaDB with ~60 GB of tables >   - InnoDB buffer pool: ~70 GB >   - Several social media sites and other complex web hosting workloads > > Baseline behavior (6.18.6) > -------------------------- > Under 6.18.6, the machine behaves as expected: > - Roughly half of the 256 GB RAM in use, half available > - Memory usage stable over time > - Swap usage negligible > - Web server and database remain responsive under normal production load > > Regression behavior (6.18.7) > ---------------------------- > After upgrading from 6.18.6 to 6.18.7, the system initially runs > normally, but after > approximately 24 hours of production load: > - Total memory usage climbs until RAM is fully consumed > - System goes ~10 GB into swap > - Web server and database stall intermittently > - Overall system responsiveness degrades severely > > Reverting to 6.18.6 immediately restores the previous stable behavior. > > Attempt to disable CONFIG_ASYNC_KERNEL_PGTABLE_FREE > --------------------------------------------------- > I attempted to disable the new async kernel page table freeing feature: > > - The symbol `CONFIG_ASYNC_KERNEL_PGTABLE_FREE` appears in `.config` > - However, it does not appear in xconfig or other configuration frontends > - Manually editing `.config` to disable it works only until the next > `make`: >   - As soon as I re-run the build, the option is silently re-enabled > - I tried to chase the Kconfig dependencies, but the chain was too > convoluted; it appears to be effectively non-user-selectable and forced > on by default for my architecture. > > From an operator perspective, this feature as currently implemented is > not workable on a busy machine like this, and the inability to disable > it makes it difficult to bisect or run with a known-good configuration. > > Current status > -------------- > - I have reverted to 6.18.6, which remains functional and stable under > the same workload. > - I have attached the '.config' for the affected 6.18.7 kernel. > - I can also collect additional data (vmstat, /proc/meminfo, slabinfo, > etc.) if you tell me what would be most useful. > > Request > ------- > 1. Is this a known issue with CONFIG_ASYNC_KERNEL_PGTABLE_FREE on large- > memory, high-load systems? > 2. Is there a supported way to disable this feature on x86_64, or could > it be made user-selectable for debugging/regression purposes? > 3. Are there specific traces or statistics you would like me to gather > when the system is in the "memory maxed + swap in use + stalls" state? > > I’m happy to run test kernels or provide additional inform