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Tue, 24 Mar 2026 15:47:00 +0000 (GMT) Message-ID: <5bf5a4f2-0505-44ef-9cea-df6ec25d9603@linux.ibm.com> Date: Tue, 24 Mar 2026 21:16:59 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 6/6] mm/memcontrol: Make memory.high tier-aware To: Gregory Price Cc: Joshua Hahn , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Qi Zheng , Axel Rasmussen , Yuanchu Xie , Wei Xu , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20260223223830.586018-1-joshua.hahnjy@gmail.com> <20260223223830.586018-7-joshua.hahnjy@gmail.com> <90749965-ebc8-43b2-92e3-baec5f6e3de0@linux.ibm.com> Content-Language: en-US From: Donet Tom In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: LVdurRN2EDTT67M7-3BJiK4bPS0nldWJ X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzI0MDExOSBTYWx0ZWRfX1s3/DoQnR89W 4OyHHua3rqv4GFjhuCfmRD+wRHyX9XpxaUnWFV0CjxWxY0+qaGst+wECvYnFNnS+P1R2KSqWsmy hF4WEydo5virXXt1dSZuQjbQRTFL7y/deW0iHb6zb7lw7UrKZyhgwzO6jn6GaMwRc6hShSUnHpU 351n0cZgj2fEY1jC0dFDy66jrgwZS/lw2F1uwYYWynlpy8vmYJJnPhbv3TYd3wGPFS7n3lwWrOR /BHtI2xJiY9+yrhU3mr25Q0irzNJL92D+PeX9sChTnAVDnyBoRk8MZtgZvbnn8Wx2HzikRkOJ/t EdQ1tMNsslsL7N6g5SohPrK6zddkVGCIyhzBsC31BUhnH8sorqp0XoIE99oC1vQI6WkYjyVWsKm D8ZU5HsUDQ2rII9G4sbSgg0TjmEHpLKzIrva4HV4Eh6b835F8OWON4m2VPi9Hd/NCzK3er7f1Z2 eWwRupQX2Pgw93AT88A== X-Authority-Analysis: v=2.4 cv=bLEb4f+Z c=1 sm=1 tr=0 ts=69c2b1fc cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=0D6tOVm0XesP3UCEPNQA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: BF40lhA_4j4DGEWWyDFDVxmTk2uqOXny X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-24_03,2026-03-23_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 adultscore=0 clxscore=1015 phishscore=0 impostorscore=0 malwarescore=0 lowpriorityscore=0 suspectscore=0 bulkscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603240119 X-Rspamd-Queue-Id: 9D25E8000E X-Stat-Signature: z4nedcgme8greski1c56w1er1t3t8kdr X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1774367253-142709 X-HE-Meta: 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 Hts0oZ/X 4U+ZiACp7vE9mVztCS0mT7deNFGHrKJtm0SZw5e1X9fL4+tHWFT8QwmrTNQVsrYmstvTWa0S32O/EdHFvUSBFH0g/9KiGjxvShRGHj6RGx+4wSuo70gsrCWCrtjcuTh1q4ehsSRPkbbYLEUT/YLJLomu45Po/x1jn7oUg/KT0F/TKEhGUSsXUOvfLO3iKLinpTe1t/RsJcXZLAmBheUPk8o7hrkf5s6nSxmXAH8d5kcVBhPXJmYerKHbxCbs9JTlHpfGFqwo2ymswDs6APuOjp7AYOMka25EpQDwN5sWnRjs/5LnLn39nD2TfmgXinhVz/KkTtmR03mDVnWmlonGLmJHia4A4ppoqNXSRxGdGnLbswavVtkNtTMHQlNzZ3qtmJ63L5jao+GP0R5HjDXlQmX0eFbnso3AmReSP Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/24/26 8:53 PM, Gregory Price wrote: > On Tue, Mar 24, 2026 at 04:21:06PM +0530, Donet Tom wrote: >> IIUC The intent of this patch is to partition cgroup memory such that >> 0 → toptier_high is backed by higher-tier memory, and >> toptier_high → max is backed by lower-tier memory. >> >> Based on this: >> >> 1.If top-tier usage exceeds toptier_high, pages should be >>   demoted to the lower tier. >> >> 2. If lower-tier usage exceeds (max - toptier_high), pages >>   should be swapped out. >> > This is not accurate and an incorrect heuristic. > > Transiently, lower-tier usage may exceed (max - toptier_high) for any > number of reasons which should not be used as signal for pushing swap. > > driving swap usage is a function of (usage > memory.high) without regard > for toptier / lowtier. > >> 3. If total memory usage exceeds max, demotion should be >>   avoided and reclaim should directly swap out pages. >> > This is also incorrect, as it would drive agingin inversions. > Demotion is a natural extension of the LRU infrastructure: > > toptier active -> toptier inactive -> lowtier inactive -> swap > > if you do (toptier inactive -> swap) you have inverted the LRU. Thanks, Gregory, for the clarification. One remaining concern is that under cgroup memory pressure, demotion to the lower tier can still happen. Since demotion does not uncharge the memcg, this could still trigger OOM. Is this an issue we should address? > > As far as I know, from testing, we retain all the existing behavior - we > are just managing a limited resource (top tier memory) to manage the > noisy-neighbor issue. So... > > >> Should we also handle cases (2) and (3) in this patch? > No, I don't think we should > > ~Gregory >