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Wed, 8 Jun 2022 08:29:55 +0000 (GMT) Message-ID: Date: Wed, 8 Jun 2022 13:59:54 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH v5 6/9] mm/demotion: Add support for removing node from demotion memory tiers Content-Language: en-US To: Ying Huang , linux-mm@kvack.org, akpm@linux-foundation.org Cc: Wei Xu , Greg Thelen , Yang Shi , Davidlohr Bueso , Tim C Chen , Brice Goglin , Michal Hocko , Linux Kernel Mailing List , Hesham Almatary , Dave Hansen , Jonathan Cameron , Alistair Popple , Dan Williams , Feng Tang , Jagdish Gediya , Baolin Wang , David Rientjes References: <20220603134237.131362-1-aneesh.kumar@linux.ibm.com> <20220603134237.131362-7-aneesh.kumar@linux.ibm.com> <81956d2e-0bfe-78ba-5ad0-f6c388c2190e@linux.ibm.com> <06d04b6588b43ca010ec78ce0dee8127193f5562.camel@intel.com> From: Aneesh Kumar K V In-Reply-To: <06d04b6588b43ca010ec78ce0dee8127193f5562.camel@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 7hKwEvUMAfuKYHmBV0IBsxOrhjtCNuim X-Proofpoint-ORIG-GUID: MY-XTz4ioShJcwhoDoswPNOzgtlkNjsz X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.874,Hydra:6.0.517,FMLib:17.11.64.514 definitions=2022-06-08_02,2022-06-07_02,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 malwarescore=0 adultscore=0 phishscore=0 bulkscore=0 lowpriorityscore=0 impostorscore=0 mlxlogscore=999 clxscore=1015 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2204290000 definitions=main-2206080035 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/8/22 1:53 PM, Ying Huang wrote: > On Wed, 2022-06-08 at 13:50 +0530, Aneesh Kumar K V wrote: >> On 6/8/22 12:29 PM, Ying Huang wrote: >>> On Fri, 2022-06-03 at 19:12 +0530, Aneesh Kumar K.V wrote: >>>> This patch adds the special string "none" as a supported memtier value >>>> that we can use to remove a specific node from being using as demotion target. >>>> >>>> For ex: >>>> :/sys/devices/system/node/node1# cat memtier >>>> 1 >>>> :/sys/devices/system/node/node1# cat ../../memtier/memtier1/nodelist >>>> 1-3 >>>> :/sys/devices/system/node/node1# echo none > memtier >>>> :/sys/devices/system/node/node1# >>>> :/sys/devices/system/node/node1# cat memtier >>>> :/sys/devices/system/node/node1# cat ../../memtier/memtier1/nodelist >>>> 2-3 >>>> :/sys/devices/system/node/node1# >>> >>> Do you have a practical use case for this? What kind of memory node >>> needs to be removed from memory tiers demotion/promotion? >>> >> >> This came up in our internal discussion. It was mentioned that there is >> a need to skip some slow memory nodes from participating in demotion. > > Again, can you provide a practical use case? Why we shouldn't demote > cold pages to these slow memory nodes? How do we use these slow memory > node? These slow memory node is slower than disk? > This was discussed in the context of memory borrowed from remote machine (aka OpenCAPI memory). In such case, we would have a memory only NUMA node which we want to avoid using for demotion. -aneesh