Harry (Hyeonggon) Yoo
Posts
564Following
103Followers
116- Linux Kernel Developer @ Oracle (Linux Kernel MM) (2025.02 ~ Present)
- Reviewer for the Linux Slab & Reverse Mapping subsystem
- Former Intern @ NVIDIA, SK Hynix, Panmnesia (Security, MM and CXL)
- B.Sc. in Computer Science & Engineering, Chungnam National University (Class of 2025)
Opinions are my own.
My interests are:
Memory Management,
Computer Architecture,
Circuit Design,
Virtualization
Harry (Hyeonggon) Yoo
hyeyoo
Edited 2 years ago
https://it.chosun.com/news/articleView.html?idxno=2023092102422
...Linux for Desktop opens new world...
...New opportunity for Korean OS in goverment PCs...
https://www.hancom.com/product/productGooroomMain.do
...Goorm OS provides secure, convenient, unique experience to desktop users...
...Goorm OS is based on debian linux...
Seriously?
I'm tired of fancy new Korea's OS platforms (K-OS) which is either 1) just another Linux distribution or 2) not Linux based but being so unusable
...Linux for Desktop opens new world...
...New opportunity for Korean OS in goverment PCs...
https://www.hancom.com/product/productGooroomMain.do
...Goorm OS provides secure, convenient, unique experience to desktop users...
...Goorm OS is based on debian linux...
Seriously?
I'm tired of fancy new Korea's OS platforms (K-OS) which is either 1) just another Linux distribution or 2) not Linux based but being so unusable
0
0
1
Harry (Hyeonggon) Yoo
repeated
repeated
nixCraft 🐧
nixCraft@mastodon.social
Edited 2 years ago
Windows: 0
Linux: 1
It is not Linux's job to stop you from shooting your foot. If you so choose to do so, then it is Linux's job to deliver Mr. Bullet to Mr. Foot in the most efficient way it knows.
2
3
1
Harry (Hyeonggon) Yoo
hyeyoo
Hmm when running builds and testcases, my machine sometimes becomes very unstable and stuck for a while.
this causes some build/test failures because git clone or job submit timeouts are exceeded.
it's very annoying and I need to fix, but I couldn't find out why. I need to setup a monitoring system...
this causes some build/test failures because git clone or job submit timeouts are exceeded.
it's very annoying and I need to fix, but I couldn't find out why. I need to setup a monitoring system...
1
0
0
Harry (Hyeonggon) Yoo
hyeyoo
Dealing with large git repositories in Jenkins
https://www.jenkins.io/files/2016/jenkins-world/large-git-repos.pdf
https://randyfay.com/content/reference-cache-repositories-speed-clones-git-clone-reference
https://www.jenkins.io/files/2016/jenkins-world/large-git-repos.pdf
https://randyfay.com/content/reference-cache-repositories-speed-clones-git-clone-reference
2
0
2
Harry (Hyeonggon) Yoo
hyeyoo
Edited 2 years ago
now I'm slowly getting how CXL manages cache coherence of device memory (HDM-{H,D,DB}). my head aches.
BTW this is a good material to grasp some important concepts of of CXL.
https://arxiv.org/abs/2306.11227
Even if it's not the final version yet.
BTW this is a good material to grasp some important concepts of of CXL.
https://arxiv.org/abs/2306.11227
Even if it's not the final version yet.
0
0
2
Harry (Hyeonggon) Yoo
hyeyoo
Edited 2 years ago
progress of this week:
#kerneltesting side project
Now my testing system can submit and run LAVA [1] test jobs automatically after jenkins [2] build!
[1] https://lava.kerneltesting.org/scheduler/alljobs
[2] https://jenkins.kerneltesting.org/job/slab/
currently it runs those:
- a subset of mm LTP testcases
- hackbench for a very short time
#kerneltesting side project
Now my testing system can submit and run LAVA [1] test jobs automatically after jenkins [2] build!
[1] https://lava.kerneltesting.org/scheduler/alljobs
[2] https://jenkins.kerneltesting.org/job/slab/
currently it runs those:
- a subset of mm LTP testcases
- hackbench for a very short time
0
1
6
Harry (Hyeonggon) Yoo
hyeyoo
Edited 2 years ago
```
As a bit of history, in the early days of PCI the spec writers anticipated cases
where PCI would actually replace the processor bus.
```
from "PCI Express Technology 3.0", MindShare
And yeah, that seems to be revived in 2019 by Intel, in the name of IAL (Intel Accelerator Link), which was renamed to CXL (Compute Express Link) later. The main reason why Intel donated IAL was to avoid making the industry fragmented. Later CXL consortium was founded and over 250 companies now contribute to the specification. Including my company! (who hired me as an intern)
As a bit of history, in the early days of PCI the spec writers anticipated cases
where PCI would actually replace the processor bus.
```
from "PCI Express Technology 3.0", MindShare
And yeah, that seems to be revived in 2019 by Intel, in the name of IAL (Intel Accelerator Link), which was renamed to CXL (Compute Express Link) later. The main reason why Intel donated IAL was to avoid making the industry fragmented. Later CXL consortium was founded and over 250 companies now contribute to the specification. Including my company! (who hired me as an intern)
0
1
3
Harry (Hyeonggon) Yoo
hyeyoo
Edited 2 years ago
it is interesting to learn how PCIe endpoints and switches implements their own protocols (similar to network protocols) for communication (PCIe transport/data link/physical layers)
but since I know very little about electronics some topics are hard to understand, like why it's difficult to increase speed in parallel bus architecture or why errors occur during transmission, or why DC components should be avoided.
but since I know very little about electronics some topics are hard to understand, like why it's difficult to increase speed in parallel bus architecture or why errors occur during transmission, or why DC components should be avoided.
3
0
0
Harry (Hyeonggon) Yoo
repeated
repeated
LWN.net is now @LWN@lwn.net
LWN@fosstodon.org[$] Progress on no-GIL CPython https://lwn.net/Articles/947138/ #LWN
0
2
1
Harry (Hyeonggon) Yoo
hyeyoo
until yesterday I didn't know that my laptop has 2 NUMA nodes, but why?
2
0
3
Harry (Hyeonggon) Yoo
hyeyoo
Edited 2 years ago
Learning how to write a LAVA test definition, but the tricker thing is to decide which tests to run to verify a kernel works fine.
Candidates:
- LTP
- KUnit
- kselftests
btw it is funny that the entire LTP suite gets killed every time it runs oom testcases. and LTP takes quite long time for a lightweight testing.
hmm... maybe run only a smaller subset of them?
Candidates:
- LTP
- KUnit
- kselftests
btw it is funny that the entire LTP suite gets killed every time it runs oom testcases. and LTP takes quite long time for a lightweight testing.
hmm... maybe run only a smaller subset of them?
0
0
1
Harry (Hyeonggon) Yoo
hyeyoo
Edited 2 years ago
Today I learned:
CXL memory can be mapped as 'System RAM' or 'Soft Reserved' by platform firmware. Or it can be dynamically provisioned by (since v6.3) CXL region driver.
And 'Soft Reserved' or dynamically provisioned CXL RAM region can be used in two ways:
1. Applications mmap() to /dev/daxX.Y files, just like traditional persistent memory devices.
2. Kernel use it as System RAM via dax_kmem driver.
And a weird fact is that when dax_kmem onlines CXL (and other performance-differentiated like pmem) memory, to ZONE_NORMAL, not ZONE_MOVABLE.
CXL memory can be mapped as 'System RAM' or 'Soft Reserved' by platform firmware. Or it can be dynamically provisioned by (since v6.3) CXL region driver.
And 'Soft Reserved' or dynamically provisioned CXL RAM region can be used in two ways:
1. Applications mmap() to /dev/daxX.Y files, just like traditional persistent memory devices.
2. Kernel use it as System RAM via dax_kmem driver.
And a weird fact is that when dax_kmem onlines CXL (and other performance-differentiated like pmem) memory, to ZONE_NORMAL, not ZONE_MOVABLE.
2
0
1
Harry (Hyeonggon) Yoo
repeated
repeated
Working on a series for 6.8 probably...
So far...
26 files changed, 39 insertions(+), 4375 deletions(-)
So far...
26 files changed, 39 insertions(+), 4375 deletions(-)
3
2
16
Harry (Hyeonggon) Yoo
hyeyoo
Edited 2 years ago
Booting the latest kernel is always fun ;)
I was hit by BUG_ON() because I enabled CONFIG_DEBUG_VIRTUAL=y.
It made my machine crash and I wrote and sent a quick hack to fix this.
https://lore.kernel.org/lkml/CAB=+i9QiJ=BXkQuCFJTh3dMXrkKQvVA2EM51Mj6SsDMimWQ71g@mail.gmail.com
Today I learned:
- Better to use proper tags for regzbot next time I report something, don't make @kernellogger do that instead of me.
- __init and __exit are compiler attributes that makes functions to be in specific ELF sections (.init.text and .exit.text), to drop portions of unused kernel code.
- When a kernel feature is built into kernel rather than built as a module, functions marked __init are dropped after initialization and functions marked __exit are dropped and never used. because you can't unload a built-in kernel feature ;)
- Some architectures drop .exit.text section at link time, but some drop at runtime. this is due to complexity of link-time reference counting between functions (? which I have no idea yet)
- On architectures that drop it at runtime, functions marked __exit are dropped in free_initmem() because .exit.text section is between __init_begin and __init_end.
- I need an automatic bisection system to save time in the future.
One piece of information I'm missing here is why it did not crash before the commit :(
I was hit by BUG_ON() because I enabled CONFIG_DEBUG_VIRTUAL=y.
It made my machine crash and I wrote and sent a quick hack to fix this.
https://lore.kernel.org/lkml/CAB=+i9QiJ=BXkQuCFJTh3dMXrkKQvVA2EM51Mj6SsDMimWQ71g@mail.gmail.com
Today I learned:
- Better to use proper tags for regzbot next time I report something, don't make @kernellogger do that instead of me.
- __init and __exit are compiler attributes that makes functions to be in specific ELF sections (.init.text and .exit.text), to drop portions of unused kernel code.
- When a kernel feature is built into kernel rather than built as a module, functions marked __init are dropped after initialization and functions marked __exit are dropped and never used. because you can't unload a built-in kernel feature ;)
- Some architectures drop .exit.text section at link time, but some drop at runtime. this is due to complexity of link-time reference counting between functions (? which I have no idea yet)
- On architectures that drop it at runtime, functions marked __exit are dropped in free_initmem() because .exit.text section is between __init_begin and __init_end.
- I need an automatic bisection system to save time in the future.
One piece of information I'm missing here is why it did not crash before the commit :(
2
0
4
Harry (Hyeonggon) Yoo
repeated
repeated
Thorsten Leemhuis (acct. 1/4)
kernellogger@fosstodon.org"[…] Instead of accepting my [#LinuxKernel] patch or guiding me towards a better solution, he went ahead and implemented his own fix, giving me credit only for reporting the issue […]
My first contribution to the [#Linux] #kernel was a really frustrating and discouraging experience, dealing with people who do not think it’s important to get proper recognition for your work. […]"
https://ariel-miculas.github.io/How-I-got-robbed-of-my-first-kernel-contribution/
1/ Side note: I sometimes wonder if…
2
3
1
Harry (Hyeonggon) Yoo
hyeyoo
Edited 2 years ago
My android phone kills the chrome app very often. It is painful that I can't see system logs. I suspect it was the OOM killer that kills it.
2
0
4
Harry (Hyeonggon) Yoo
repeated
repeated
Liam @ GamingOnLinux 🐧🎮
gamingonlinux@mastodon.socialRaspberry Pi 5 announced - still tiny, much more powerful https://www.gamingonlinux.com/2023/09/raspberry-pi-5-announced-still-tiny-much-more-powerful/
0
2
1
Harry (Hyeonggon) Yoo
repeated
repeated
Dare Obasanjo
carnage4life@mas.toWelcome to the cycle of generative AI making search worse.
Quora uses ChatGPT which hallucinates an answer to a nonsense question.
Google Search picks up this nonsense answer from Quora which has high page rank and treats it as an instant answer.
9
11
3