Re: [RFC PATCH V1 0/5] mm/damon: Add NUMA access statistics function support

From: Xin Hao
Date: Thu Feb 17 2022 - 21:21:36 EST

Hi SeongJae:

On 2/17/22 4:29 PM, SeongJae Park wrote:
+ David Rientjes, who has shown interest[1] in this topic.

[1] https://lore.kernel.org/linux-mm/bcc8d9a0-81d-5f34-5e4-fcc28eb7ce@xxxxxxxxxx/

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Hi Xin,


Thank you always for great patches!

On Wed, 16 Feb 2022 16:30:36 +0800 Xin Hao <xhao@xxxxxxxxxxxxxxxxx> wrote:

On today's cloud computing service scenario, NUMA (non uniform memory access)
architecture server has been applied on a large scale. Using Damon function,
it can easily and lightweight identify hot and cold memory, but it can not
display the situation of locale and remote NUMA memory access.

The purpose of these serie patches is to identify the situation of NUMA access
in combination with DAMON, especially for remote NUMA access in hot memory.
We hope to detect this situation in the data center and use page migration or
multi backup page technology to optimize the behavior of memory access.

So next, we will further improve Damon NUMA function:
1. Support hugtlbfs NUMA access statistics.
2. Add the DAMO tool to parse NUMA local & remote in "damon_region" support.
3. For hot memory remote NUMA access, support page migration or multi backup page.

About DAMON correctness of numa access statistics
We wrote a test case, allocate about 1G memory, and use numa_alloc(), set 512M in
NUMA node0 and 512M in NUMA node1, and The test case alternately accesses the 1G of memory.

We used "perf record -e damon:damon_aggregated" and "perf script"
cmd to obtain data, like this:
kdamond.0 target_id=0 nr_regions=10 281473056325632-281473127964672:: 12 0 5243 5513
kdamond.0 target_id=0 nr_regions=10 281473127964672-281473238028288: 8 1 5427 5399
...
kdamond.0 target_id=0 nr_regions=10 281473056325632-281473127964672: 9 3 7669 7632
kdamond.0 target_id=0 nr_regions=10 281473127964672-281473238028288: 7 2 7913 7892

And compared with numastat like this:
Per-node process memory usage (in MBs) for PID 111676 (lt-numademo)
Node 0 Node 1 Node 2
--------------- --------------- ---------------
Huge 0.00 0.00 0.00
Heap 0.02 0.00 0.00
Stack 0.01 0.00 0.00
Private 565.24 564.00 0.00
---------------- --------------- --------------- ---------------
Total 565.27 564.00 0.00
This comparison can determine the accuracy of Damon NUMA memory access statistics.

About the impact of DAMON NUMA access on Performance
During the benchmakr test, we found that the MBW benchmark memcpy test item
will cause about 3% performance degradation, and there is no performance degradation
in other benchmarks.
So we added "numa_stat" switch in DAMON dbgfs interface, turn on this switch when NUMA access
statistics is required.


Xin Hao (5):
mm/damon: Add NUMA local and remote variables in 'damon_region'
mm/damon: Add 'damon_region' NUMA fault simulation support
mm/damon: Add 'damon_region' NUMA access statistics core
implementation
mm/damon/dbgfs: Add numa simulate switch
mm/damon/tracepoint: Add 'damon_region' NUMA access statistics support

include/linux/damon.h | 25 ++++++++++
include/trace/events/damon.h | 9 +++-
mm/damon/core.c | 94 +++++++++++++++++++++++++++++++++++-
mm/damon/dbgfs.c | 70 ++++++++++++++++++++++++---
mm/damon/paddr.c | 25 ++++++++--
mm/damon/prmtv-common.c | 44 +++++++++++++++++
mm/damon/prmtv-common.h | 3 ++
mm/damon/vaddr.c | 45 ++++++++++-------
mm/huge_memory.c | 5 ++
mm/memory.c | 5 ++
10 files changed, 292 insertions(+), 33 deletions(-)
I'd like to comment on the high level design at the moment. To my
understanding, this patchset extends DAMON core and monitoring operations for
virtual address spaces (vaddr) and the physical address space (paddr) to
monitor NUMA-local/remote accesses via PROT_NONE and page faults mechanism.

The underlying mechanism for NUMA-local/remote accesses (PROT_NONE and page
fault) looks ok to me. But, changes to the core and vaddr/paddr operations
looks unnecessary, to me. That's also not for general use cases.
You are right, adding NUMA access statistics does make the PA & VA codes look confusing。

I think it would be simpler to implment more monitoring operations for NUMA
monitoring use case (one for NUMA-local accesses accounting and another one for
NUMA-remote accesses accounting), alongside vaddr and paddr. Then, users could
configure DAMON to have three monitoring contexts (one with vaddr ops, second
one with numa-local ops, and third one with numa-remote ops), run those
concurrently, then show the three results and make some decisions like
migrations.

Thanks for your advice, I will implement these in the next version, But from my understanding or maybe

I didn't get what you were thinking, I think only one monitor context is needed for NUMA Local & Remote,

Do not need a separate implementation like "numa_local_ops" and "numa_remote_ops", just set "numa_access_ops" is ok.


One additional advantage of this approach is that the accuracy for
NUMA-local/remote accessed could be better, because the contexts configured to
use NUMA-local/remote monitoring ops will do the regions adjustment with
NUMA-local/remote accesses (to my understanding, this patchset let regions have
NUMA-local/remote accesses counter in addition to the total one, but still use
only the total one for the regions adjustment).

If I'm missing something, please let me know.


Thanks,
SJ

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2.27.0

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Best Regards!
Xin Hao