linux-kernel - Re: [PATCH v5 0/2] sched/numa: Skip VMA scanning on memory pinned to one NUMA node via cpuset.mems

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Message-ID: <57892439-7683-43b7-9b03-4553737273b7@linux.ibm.com>
Date: Thu, 24 Apr 2025 12:35:36 +0530
From: Venkat Rao Bagalkote <venkat88@...ux.ibm.com>
To: Libo Chen <libo.chen@...cle.com>, akpm@...ux-foundation.org,
        rostedt@...dmis.org, peterz@...radead.org, mgorman@...e.de,
        mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
        tj@...nel.org, llong@...hat.com
Cc: sraithal@....com, kprateek.nayak@....com, raghavendra.kt@....com,
        yu.c.chen@...el.com, tim.c.chen@...el.com, vineethr@...ux.ibm.com,
        chris.hyser@...cle.com, daniel.m.jordan@...cle.com,
        lorenzo.stoakes@...cle.com, mkoutny@...e.com, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/2] sched/numa: Skip VMA scanning on memory pinned to
 one NUMA node via cpuset.mems


On 24/04/25 8:15 am, Libo Chen wrote:
> v1->v2:
> 1. add perf improvment numbers in commit log. Yet to find perf diff on
> will-it-scale, so not included here. Plan to run more workloads.
> 2. add tracepoint.
> 3. To peterz's comment, this will make it impossible to attract tasks to
> those memory just like other VMA skippings. This is the current
> implementation, I think we can improve that in the future, but at the
> moment it's probabaly better to keep it consistent.
>
> v2->v3:
> 1. add enable_cpuset() based on Mel's suggestion but again I think it's
> redundant.
> 2. print out nodemask with %*p.. format in the tracepoint.
>
> v3->v4:
> 1. fix an unsafe dereference of a pointer to content not on ring buffer,
> namely mem_allowed_ptr in the tracepoint.
>
> v4->v5:
> 1. add BUILD_BUG_ON() in TP_fast_assign() to guard against future
> changes (particularly in size) in nodemask_t.
>
> Libo Chen (2):
>    sched/numa: Skip VMA scanning on memory pinned to one NUMA node via
>      cpuset.mems
>    sched/numa: Add tracepoint that tracks the skipping of numa balancing
>      due to cpuset memory pinning
>
>   include/trace/events/sched.h | 33 +++++++++++++++++++++++++++++++++
>   kernel/sched/fair.c          |  9 +++++++++
>   2 files changed, 42 insertions(+)
>
Hello Libo,


For some reason I am not able to apply this patch. I am trying to test 
the boot warning[1].

I am trying to apply on top of next-20250423. Below is the error. Am I 
missing anything?

[1]: https://lore.kernel.org/all/20250422205740.02c4893a@canb.auug.org.au/

Error:

git am -i 
v5_20250423_libo_chen_sched_numa_skip_vma_scanning_on_memory_pinned_to_one_numa_node_via_cpuset_mems.mbx
Commit Body is:
--------------------------
sched/numa: Skip VMA scanning on memory pinned to one NUMA node via 
cpuset.mems

When the memory of the current task is pinned to one NUMA node by cgroup,
there is no point in continuing the rest of VMA scanning and hinting page
faults as they will just be overhead. With this change, there will be no
more unnecessary PTE updates or page faults in this scenario.

We have seen up to a 6x improvement on a typical java workload running on
VMs with memory and CPU pinned to one NUMA node via cpuset in a two-socket
AARCH64 system. With the same pinning, on a 18-cores-per-socket Intel
platform, we have seen 20% improvment in a microbench that creates a
30-vCPU selftest KVM guest with 4GB memory, where each vCPU reads 4KB
pages in a fixed number of loops.

Signed-off-by: Libo Chen <libo.chen@...cle.com>
Tested-by: Chen Yu <yu.c.chen@...el.com>
Tested-by: K Prateek Nayak <kprateek.nayak@....com>
--------------------------
Apply? [y]es/[n]o/[e]dit/[v]iew patch/[a]ccept all: a
Applying: sched/numa: Skip VMA scanning on memory pinned to one NUMA 
node via cpuset.mems
error: patch failed: kernel/sched/fair.c:3329
error: kernel/sched/fair.c: patch does not apply
Patch failed at 0001 sched/numa: Skip VMA scanning on memory pinned to 
one NUMA node via cpuset.mems


Regards,

Venkat.