On 8/15/22 8:09 AM, Huang, Ying wrote: > "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> writes: > >> By default, all nodes are assigned to the default memory tier which >> is the memory tier designated for nodes with DRAM >> >> Set dax kmem device node's tier to slower memory tier by assigning >> abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE. Low-level drivers >> like papr_scm or ACPI NFIT can initialize memory device type to a >> more accurate value based on device tree details or HMAT. If the >> kernel doesn't find the memory type initialized, a default slower >> memory type is assigned by the kmem driver. >> >> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> >> --- >> drivers/dax/kmem.c | 42 +++++++++++++++-- >> include/linux/memory-tiers.h | 42 ++++++++++++++++- >> mm/memory-tiers.c | 91 +++++++++++++++++++++++++++--------- >> 3 files changed, 149 insertions(+), 26 deletions(-) >> >> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c >> index a37622060fff..d88814f1c414 100644 >> --- a/drivers/dax/kmem.c >> +++ b/drivers/dax/kmem.c >> @@ -11,9 +11,17 @@ >> #include <linux/fs.h> >> #include <linux/mm.h> >> #include <linux/mman.h> >> +#include <linux/memory-tiers.h> >> #include "dax-private.h" >> #include "bus.h" >> >> +/* >> + * Default abstract distance assigned to the NUMA node onlined >> + * by DAX/kmem if the low level platform driver didn't initialize >> + * one for this NUMA node. >> + */ >> +#define MEMTIER_DEFAULT_DAX_ADISTANCE (MEMTIER_ADISTANCE_DRAM * 2) > > If my understanding were correct, this is targeting Optane DCPMM for > now. The measured results in the following paper is, > > https://arxiv.org/pdf/2002.06018.pdf > > Section: 2.1 Read/Write Latencies > > " > For read access, the latency of DCPMM was 400.1% higher than that of > DRAM. For write access, it was 407.1% higher. > " > > Section: 2.2 Read/Write Bandwidths > > " > For read access, the throughput of DCPMM was 37.1% of DRAM. For write > access, it was 7.8% > " > > According to the above data, I think the MEMTIER_DEFAULT_DAX_ADISTANCE > can be "5 * MEMTIER_ADISTANCE_DRAM". > If we look at mapping every 100% increase in latency as a memory tier, we essentially will have 4 memory tier here. Each memory tier is covering a range of abstract distance 128. which makes a total adistance increase from MEMTIER_ADISTANCE_DRAM by 512. This puts DEFAULT_DAX_DISTANCE at 1024 or MEMTIER_ADISTANCE_DRAM * 2 -aneesh
