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Date: Fri, 3 Jun 2022 14:10:47 +0530 From: Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com> To: Jonathan Cameron <Jonathan.Cameron@...wei.com> Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, Huang Ying <ying.huang@...el.com>, Greg Thelen <gthelen@...gle.com>, Yang Shi <shy828301@...il.com>, Davidlohr Bueso <dave@...olabs.net>, Tim C Chen <tim.c.chen@...el.com>, Brice Goglin <brice.goglin@...il.com>, Michal Hocko <mhocko@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Hesham Almatary <hesham.almatary@...wei.com>, Dave Hansen <dave.hansen@...el.com>, Alistair Popple <apopple@...dia.com>, Dan Williams <dan.j.williams@...el.com>, Feng Tang <feng.tang@...el.com>, Jagdish Gediya <jvgediya@...ux.ibm.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, David Rientjes <rientjes@...gle.com> Subject: Re: [RFC PATCH v4 2/7] mm/demotion: Expose per node memory tier to sysfs On 5/27/22 7:45 PM, Jonathan Cameron wrote: > On Fri, 27 May 2022 17:55:23 +0530 > "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> wrote: > >> From: Jagdish Gediya <jvgediya@...ux.ibm.com> >> >> Add support to read/write the memory tierindex for a NUMA node. >> >> /sys/devices/system/node/nodeN/memtier >> >> where N = node id >> >> When read, It list the memory tier that the node belongs to. >> >> When written, the kernel moves the node into the specified >> memory tier, the tier assignment of all other nodes are not >> affected. >> >> If the memory tier does not exist, writing to the above file >> create the tier and assign the NUMA node to that tier. > creates > > There was some discussion in v2 of Wei Xu's RFC that what matter > for creation is the rank, not the tier number. > > My suggestion is move to an explicit creation file such as > memtier/create_tier_from_rank > to which writing the rank gives results in a new tier > with the next device ID and requested rank. I think the below workflow is much simpler. :/sys/devices/system# cat memtier/memtier1/nodelist 1-3 :/sys/devices/system# cat node/node1/memtier 1 :/sys/devices/system# ls memtier/memtier* nodelist power rank subsystem uevent /sys/devices/system# ls memtier/ default_rank max_tier memtier1 power uevent :/sys/devices/system# echo 2 > node/node1/memtier :/sys/devices/system# :/sys/devices/system# ls memtier/ default_rank max_tier memtier1 memtier2 power uevent :/sys/devices/system# cat memtier/memtier1/nodelist 2-3 :/sys/devices/system# cat memtier/memtier2/nodelist 1 :/sys/devices/system# ie, to create a tier we just write the tier id/tier index to node/nodeN/memtier file. That will create a new memory tier if needed and add the node to that specific memory tier. Since for now we are having 1:1 mapping between tier index to rank value, we can derive the rank value from the memory tier index. For dynamic memory tier support, we can assign a rank value such that new memory tiers are always created such that it comes last in the demotion order. -aneesh
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