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Following
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Followers
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A relatively new professional kernel hacker, born in August 6, 2000, and living in Korea (South!).

- Linux Kernel Developer @ Oracle (Linux Kernel MM) (2025.02 ~ Present)
- Reviewer for the Linux Slab 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
hyeyoo

Harry (Hyeonggon) Yoo

Edited 1 year ago
Making a small progress on one of my TODOs: run automatic builds & tests using CI tools for MM development kernels

This is a jenkins configuration matrix specially targeting SLUB to cover various SLUB configurations. Only boot test is done atm.

There are many milestones on this project, which demands more time :P
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hyeyoo

Harry (Hyeonggon) Yoo

Reply to @ljs
@ljs oh mate...
you are right
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hyeyoo

Harry (Hyeonggon) Yoo

Reply to @vbabka
@vbabka
haven't watched it yet, but I knew it! the poster was epic as well.
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hyeyoo

Harry (Hyeonggon) Yoo

Me with my friends
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hyeyoo

Harry (Hyeonggon) Yoo

Edited 1 year ago
When there are no free pages in free list of the requested order, buddy allocator splits a larger page into smaller ones, and allocates a one of the split pages.

TIL: The way buddy splits large pages (and allocating first or last part of a large page) during the expand() function significantly impacts the mergability of the scatter-gather list for IO. The likeliness that pages are allocated in PFN order is important for mergability. This is so subtle and I didn't realize this :(

Consider a scenario where there is only an order 2 block, and four order 0 requests are served. In the diagram above, they are allocated in PFN order, while in the other diagram, they are allocated in the reverse order.

https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=c75b81a5da09be94099cf7b46bdb32fedc8ce71a

And in the history this thing has introduced a regression because the order was not preserved (by mistake) when pages are allocated from PCP lists with __GFP_COLD ;)

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e084b2d95e48b31aa45f9c49ffc6cdae8bdb21d4
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hyeyoo

Harry (Hyeonggon) Yoo

something big is coming
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hyeyoo

Harry (Hyeonggon) Yoo

Edited 1 year ago
damn it's too hot
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hyeyoo

Harry (Hyeonggon) Yoo

Reply to @krzk
@krzk @Andi I love draft beers but the most common beers in a casual restaurant in Korea are these ;) (bottled beers)
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hyeyoo

Harry (Hyeonggon) Yoo

Reply to @ljs
@ljs @vbabka LOL it's sliced cheddar cheese, a real one! (very common in Korea)
is it that terrible?
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hyeyoo

Harry (Hyeonggon) Yoo

Beef tartare
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hyeyoo

Harry (Hyeonggon) Yoo

Reply to @hyeyoo
Remote node access latency is approximately 40% higher than that of the local node, and the throughput for remote nodes is only half of that for local nodes.
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hyeyoo

Harry (Hyeonggon) Yoo

Edited 1 year ago
I've just built my first 2 socket server (36C/72T, DDR4 256GB ECC/REG RAM) for experimenting with NUMA.
It's an old xeon server (Broadwell), but enough to play with!
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hyeyoo

Harry (Hyeonggon) Yoo

How am I supposed to take it out
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hyeyoo

Harry (Hyeonggon) Yoo

poor photographer
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hyeyoo

Harry (Hyeonggon) Yoo

someone took a bite out of my slipper.
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hyeyoo

Harry (Hyeonggon) Yoo

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hyeyoo

Harry (Hyeonggon) Yoo

Edited 1 year ago
I bought a new graphics card yesterday, and it came with a freebie. now my machine hangs whenever I boot a kernel with lockdep enabled.

Here is the link to the issue I posted on GitLab: https://gitlab.freedesktop.org/drm/nouveau/-/issues/237

BTW does DRM folks prefer using GitLab or the mailing list?
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hyeyoo

Harry (Hyeonggon) Yoo

I want NVIDIA's proprietary GPU drivers 🥲
nouveau does not support virtual GPUs...
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hyeyoo

Harry (Hyeonggon) Yoo

Edited 1 year ago
I was refreshing my zsdesc patch series but encountered unrelated bug while testing (I bought new RAM so it must be software bug...)

Fortunately it was bisectable and I'm writing a report about it
Not sure if people will welcome an oops image instead of text format.
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hyeyoo

Harry (Hyeonggon) Yoo

Reply to @hyeyoo
@ljs gotcha!
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