Donet Tom <donettom@xxxxxxxxxxxxx> writes:
> On 2/19/24 17:37, Michal Hocko wrote:
>> On Sat 17-02-24 01:31:35, Donet Tom wrote:
>>> commit bda420b98505 ("numa balancing: migrate on fault among multiple bound
>>> nodes") added support for migrate on protnone reference with MPOL_BIND
>>> memory policy. This allowed numa fault migration when the executing node
>>> is part of the policy mask for MPOL_BIND. This patch extends migration
>>> support to MPOL_PREFERRED_MANY policy.
>>>
>>> Currently, we cannot specify MPOL_PREFERRED_MANY with the mempolicy flag
>>> MPOL_F_NUMA_BALANCING. This causes issues when we want to use
>>> NUMA_BALANCING_MEMORY_TIERING. To effectively use the slow memory tier,
>>> the kernel should not allocate pages from the slower memory tier via
>>> allocation control zonelist fallback. Instead, we should move cold pages
>>> from the faster memory node via memory demotion. For a page allocation,
>>> kswapd is only woken up after we try to allocate pages from all nodes in
>>> the allocation zone list. This implies that, without using memory
>>> policies, we will end up allocating hot pages in the slower memory tier.
>>>
>>> MPOL_PREFERRED_MANY was added by commit b27abaccf8e8 ("mm/mempolicy: add
>>> MPOL_PREFERRED_MANY for multiple preferred nodes") to allow better
>>> allocation control when we have memory tiers in the system. With
>>> MPOL_PREFERRED_MANY, the user can use a policy node mask consisting only
>>> of faster memory nodes. When we fail to allocate pages from the faster
>>> memory node, kswapd would be woken up, allowing demotion of cold pages
>>> to slower memory nodes.
>>>
>>> With the current kernel, such usage of memory policies implies we can't
>>> do page promotion from a slower memory tier to a faster memory tier
>>> using numa fault. This patch fixes this issue.
>>>
>>> For MPOL_PREFERRED_MANY, if the executing node is in the policy node
>>> mask, we allow numa migration to the executing nodes. If the executing
>>> node is not in the policy node mask but the folio is already allocated
>>> based on policy preference (the folio node is in the policy node mask),
>>> we don't allow numa migration. If both the executing node and folio node
>>> are outside the policy node mask, we allow numa migration to the
>>> executing nodes.
>> The feature makes sense to me. How has this been tested? Do you have any
>> numbers to present?
>
> Hi Michal
>
> I have a test program which allocate memory on a specified node and
> trigger the promotion or migration (Keep accessing the pages).
>
> Without this patch if we set MPOL_PREFERRED_MANY promotion or migration was not happening
> with this patch I could see pages are getting migrated or promoted.
>
> My system has 2 CPU+DRAM node (Tier 1) and 1 PMEM node(Tier 2). Below
> are my test results.
>
> In below table N0 and N1 are Tier1 Nodes. N6 is the Tier2 Node.
> Exec_Node is the execution node, Policy is the nodes in nodemask and
> "Curr Location Pages" is the node where pages present before migration
> or promotion start.
>
> Tests Results
> ------------------
> Scenario 1: if the executing node is in the policy node mask
> ================================================================================
> Exec_Node Policy Curr Location Pages Observations
> ================================================================================
> N0 N0 N1 N6 N1 Pages Migrated from N1 to N0
> N0 N0 N1 N6 N6 Pages Promoted from N6 to N0
> N0 N0 N1 N1 Pages Migrated from N1 to N0
> N0 N0 N1 N6 Pages Promoted from N6 to N0
>
> Scenario 2: If the folio node is in policy node mask and Exec node not in policy node mask
> ================================================================================
> Exec_Node Policy Curr Location Pages Observations
> ================================================================================
> N0 N1 N6 N1 Pages are not Migrating to N0
> N0 N1 N6 N6 Pages are not migration to N0
> N0 N1 N1 Pages are not Migrating to N0
>
> Scenario 3: both the folio node and executing node are outside the policy nodemask
> ==============================================================================
> Exec_Node Policy Curr Location Pages Observations
> ==============================================================================
> N0 N1 N6 Pages Promoted from N6 to N0
> N0 N6 N1 Pages Migrated from N1 to N0
>
Please use some benchmarks (e.g., redis + memtier) and show the
proc-vmstat stats and benchamrk score.
Not part of the kernel series, but don't forget to submit patches to the
man pages project and numactl tool to let users use it.
--
Best Regards,
Huang, Ying
> Thanks
> Donet Tom
>
>>
>>> Signed-off-by: Aneesh Kumar K.V (IBM) <aneesh.kumar@xxxxxxxxxx>
>>> Signed-off-by: Donet Tom <donettom@xxxxxxxxxxxxx>
>>> ---
>>> mm/mempolicy.c | 28 ++++++++++++++++++++++++++--
>>> 1 file changed, 26 insertions(+), 2 deletions(-)
>> I haven't spotted anything obviously wrong in the patch itself but I
>> admit this is not an area I am actively familiar with so I might be
>> missing something.
