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client-ip=165.204.84.17; helo=satlexmb08.amd.com; pr=C Received: from satlexmb08.amd.com (165.204.84.17) by SJ5PEPF00000206.mail.protection.outlook.com (10.167.244.39) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.428.7 via Frontend Transport; Wed, 16 Sep 2026 03:08:24 +0000 Received: from satlexmb07.amd.com (10.181.42.216) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.49; Tue, 15 Sep 2026 22:08:23 -0500 Received: from [192.168.0.152] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server id 15.2.2562.49 via Frontend Transport; Tue, 15 Sep 2026 22:08:16 -0500 Message-ID: Date: Wed, 16 Sep 2026 08:38:17 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 0/8] mm: Hot page tracking and promotion infrastructure To: Joshua Hahn CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , References: <20260911210859.1359875-1-joshua.hahnjy@gmail.com> Content-Language: en-US From: Bharata B Rao In-Reply-To: <20260911210859.1359875-1-joshua.hahnjy@gmail.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 4yFLT0s8OELjPqFum2EEH2LAUeyCsLsEvICBVM3csRHztXlZ27PVqOTVDgiIEfY2cMTZ+wpvNGHtnXuqCbZNlzNh/ZX8ST8Js7QlnHrlUD4FwtY/+ftXpSyO+pfc58e/DkET86VJJOaZP9pLLxNKV0uSfTSsIVekPGvbyDxU31xKBxhBvY3wOOEe109fOggJNRWwAy9rOUIo4QDHVMz60YRRLOgDparbH8Hl+fCVGV8J/ZCHb/oMmvmhlFas/1tRkwGVgKVI5NyPgepJ/YCVJJuIuoL0eRgnPqZ1iTSlKdlMEUXdU967J6AtasNP3JqLSZN0ORYVwE0qttNrLyr99bIJYLiZgGj3fm6MVs1NdN2aa9OOCr48FFJMBkjWCEWppdck7TNqFHeBUXu4FnjbH6LXIeuenswhMiEj2i2fQivkPy40J3KgnHfqo8LAoV71 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Sep 2026 03:08:24.5758 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: e1a53a73-fb35-42b5-2a15-08df139fc5ac X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ5PEPF00000206.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB7571 On 12-Sep-26 2:38 AM, Joshua Hahn wrote: > Hi Bharata, > > We've been testing pghot in a Meta kernel with worklaods to try and see > what the performance characteristics look like. I wanted to report > some of the findings that we've found in our testing. Note that these > results are from a modified kernel that has my tiered memcg series [1] > backported, as well as Gregory's numa balancing scanning fixes [2] > as well. Hi Joshua, Thanks for testing pghot with your workload! > > - Without tuning and using the default tunables that pghot comes with, > we've found around a slight performance regression against raw NUMAB2. > This was being run on a host with 750G DRAM and 250G CXL. pghot promotes on 2nd access by default since pghot_freq_threshold is 2 by default. This will result in slower promotions compared to NUMAB2 which promotes on 1st access. Could you please try with setting pghot_freq_threshold to 1? I think I should make the default as 1 going forward. In any case, will it be possible to provide more information on what your workloads are, and the exact performance metrics? Any representative workload that can be substituted to reproduce this behaviour can also help. And when you say slight perf regression, how much is it exactly? > - However, we've found lower pgscan_direct, pgpromote, and pgdemote > rates as well. > - We've seen PSI dramatically drop on the host as well as the promotion > happens asynchronously. That's good to see. > - I also found a bug where the kmigrated thread isn't created for nodes > that are onlined later after boot, like CXL nodes that get onlined > with memory later on. I've been using a small hack commit in > pghot_memhp_callback that just checks for the MEM_ONLINE case and > spawns a kmigrated thread. I will take care of this scenario (CXL node online after boot) in my next posting. > > Finally, we've seen some issues with pghot causing userspace crashes, > which leads us to believe that there might be some bugs that manifest > in userspace as well (we have not been able to find out where in pghot > these bugs are introduced). That's something I have never seen till now with any of the benchmarks that I have run. Any kernel messages attributing the failure to pghot? Anything attributable to access reporting or kmigrated threads? Any clues from coredump or gdb debug of userspace crash? Were you running your workloads as part of a non-root memcg? Do you see these failures without [1] and/or [2] ? > > Thanks for working on pghot! > Joshua > > [1] https://lore.kernel.org/all/20260807202059.2620949-1-joshua.hahnjy@gmail.com/ > [2] https://lore.kernel.org/all/20260911001826.2109390-1-gourry@gourry.net/ Regards, Bharata.