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Date: Fri, 15 Dec 2023 13:02:59 +0800 From: "Huang, Ying" <ying.huang@...el.com> To: <sthanneeru.opensrc@...ron.com> Cc: <linux-cxl@...r.kernel.org>, <linux-mm@...ck.org>, <sthanneeru@...ron.com>, <aneesh.kumar@...ux.ibm.com>, <dan.j.williams@...el.com>, <gregory.price@...verge.com>, <mhocko@...e.com>, <tj@...nel.org>, <john@...alactic.com>, <emirakhur@...ron.com>, <vtavarespetr@...ron.com>, <Ravis.OpenSrc@...ron.com>, <Jonathan.Cameron@...wei.com>, <linux-kernel@...r.kernel.org> Subject: Re: [RFC PATCH v2 0/2] Node migration between memory tiers <sthanneeru.opensrc@...ron.com> writes: > From: Srinivasulu Thanneeru <sthanneeru.opensrc@...ron.com> > > The memory tiers feature allows nodes with similar memory types > or performance characteristics to be grouped together in a > memory tier. However, there is currently no provision for > moving a node from one tier to another on demand. > > This patch series aims to support node migration between tiers > on demand by sysadmin/root user using the provided sysfs for > node migration. > > To migrate a node to a tier, the corresponding node’s sysfs > memtier_override is written with target tier id. > > Example: Move node2 to memory tier2 from its default tier(i.e 4) > > 1. To check current memtier of node2 > $cat /sys/devices/system/node/node2/memtier_override > memory_tier4 > > 2. To migrate node2 to memory_tier2 > $echo 2 > /sys/devices/system/node/node2/memtier_override > $cat /sys/devices/system/node/node2/memtier_override > memory_tier2 > > Usecases: > > 1. Useful to move cxl nodes to the right tiers from userspace, when > the hardware fails to assign the tiers correctly based on > memorytypes. > > On some platforms we have observed cxl memory being assigned to > the same tier as DDR memory. This is arguably a system firmware > bug, but it is true that tiers represent *ranges* of performance > and we believe it's important for the system operator to have > the ability to override bad firmware or OS decisions about tier > assignment as a fail-safe against potential bad outcomes. > > 2. Useful if we want interleave weights to be applied on memory tiers > instead of nodes. > In a previous thread, Huang Ying <ying.huang@...el.com> thought > this feature might be useful to overcome limitations of systems > where nodes with different bandwidth characteristics are grouped > in a single tier. > https://lore.kernel.org/lkml/87a5rw1wu8.fsf@yhuang6-desk2.ccr.corp.intel.com/ > > ============= > Version Notes: > > V2 : Changed interface to memtier_override from adistance_offset. > memtier_override was recommended by > 1. John Groves <john@...alactic.com> > 2. Ravi Shankar <ravis.opensrc@...ron.com> > 3. Brice Goglin <Brice.Goglin@...ia.fr> It appears that you ignored my comments for V1 as follows ... https://lore.kernel.org/lkml/87o7f62vur.fsf@yhuang6-desk2.ccr.corp.intel.com/ https://lore.kernel.org/lkml/87jzpt2ft5.fsf@yhuang6-desk2.ccr.corp.intel.com/ https://lore.kernel.org/lkml/87a5qp2et0.fsf@yhuang6-desk2.ccr.corp.intel.com/ -- Best Regards, Huang, Ying > V1 : Introduced adistance_offset sysfs. > > ============= > > Srinivasulu Thanneeru (2): > base/node: Add sysfs for memtier_override > memory tier: Support node migration between tiers > > Documentation/ABI/stable/sysfs-devices-node | 7 ++ > drivers/base/node.c | 47 ++++++++++++ > include/linux/memory-tiers.h | 11 +++ > include/linux/node.h | 11 +++ > mm/memory-tiers.c | 85 ++++++++++++--------- > 5 files changed, 125 insertions(+), 36 deletions(-)
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