[lkml]   [2022]   [Jun]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v5 4/9] mm/demotion: Build demotion targets based on explicit memory tiers
On 6/8/22 12:20 PM, Ying Huang wrote:
> On Fri, 2022-06-03 at 19:12 +0530, Aneesh Kumar K.V wrote:
>> This patch switch the demotion target building logic to use memory tiers
>> instead of NUMA distance. All N_MEMORY NUMA nodes will be placed in the
>> default tier 1 and additional memory tiers will be added by drivers like
>> dax kmem.
>> This patch builds the demotion target for a NUMA node by looking at all
>> memory tiers below the tier to which the NUMA node belongs. The closest node
>> in the immediately following memory tier is used as a demotion target.
>> Since we are now only building demotion target for N_MEMORY NUMA nodes
>> the CPU hotplug calls are removed in this patch.
>> The rank approach allows us to keep memory tier device IDs stable even if there
>> is a need to change the tier ordering among different memory tiers. e.g. DRAM
>> nodes with CPUs will always be on memtier1, no matter how many tiers are higher
>> or lower than these nodes. A new memory tier can be inserted into the tier
>> hierarchy for a new set of nodes without affecting the node assignment of any
>> existing memtier, provided that there is enough gap in the rank values for the
>> new memtier.
>> The absolute value of "rank" of a memtier doesn't necessarily carry any meaning.
>> Its value relative to other memtiers decides the level of this memtier in the tier
>> hierarchy.
>> For now, This patch supports hardcoded rank values which are 300, 200, & 100 for
>> memory tiers 0,1 & 2 respectively.
>> Below is the sysfs interface to read the rank values of memory tier,
>> /sys/devices/system/memtier/memtierN/rank
>> This interface is read only for now. Write support can be added when there is
>> a need of flexibility of more number of memory tiers(> 3) with flexibile ordering
>> requirement among them.
>> Suggested-by: Wei Xu <>
>> Signed-off-by: Aneesh Kumar K.V <>
>> ---
>>  include/linux/memory-tiers.h | 5 +
>>  include/linux/migrate.h | 13 --
>>  mm/memory-tiers.c | 269 ++++++++++++++++++++++++
>>  mm/migrate.c | 394 -----------------------------------
>>  mm/vmstat.c | 4 -
>>  5 files changed, 274 insertions(+), 411 deletions(-)
> It appears that you moved some code from migrate.c to memory-tiers.c and
> change them. If so, please separate the change. That is, one patch
> only move the code, the other change the code. This will make it easier
> to find out what is changed.

That was how it was done in earlier version. That is we did change
establish_migration within the same file. The changes we are doing here
was so different that it was mentioned that it gets very hard to review
in a context diff. Hence this patch where we killed the old code and did
the new code in memory-tiers.c. I could still move the code to
memory-tiers.c and do the changes on top of that. Infact I do have a
patch that does similar code movement in the series. But the diff was
not useful for an easy review.


 \ /
  Last update: 2022-06-08 11:05    [W:0.087 / U:0.348 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site