| 21 Nov 2025 |
 John Ericson | split libcmd into store layer and not store layer parts | 17:10:40 |
|  isabel changed their profile picture. | 18:13:57 |
 Rutile (Commentator2.0) feel free to ping | https://gerrit.lix.systems/c/lix/+/4605
its merged 🎉
| 18:34:13 |
 raitobezarius | I looked and I may have missed it but I still see special cases in libcmd on master. | 18:41:27 |
|  mzero joined the room. | 20:37:43 |
| mzero | did the special casing for small lists get removed? there are still comments that refer to it, but I'm not seeing it in the code (though I could just be missing it) | 20:54:15 |
| raitobezarius | removed, indeed | 20:54:40 |
| raitobezarius | did you notice something problematic for small lists? | 20:54:48 |
| mzero | no, I was just looking at the string changes in the release notes and noticed it. is there any perforce impact from it? I assume lists with exactly 2 elems aren't that common, but I'm still curious. | 20:59:59 |
| raitobezarius | AFAIK, this optimization is noise when we looked | 21:07:47 |
| raitobezarius | Lists with 2 elems are usually pairs in Nixlang | 21:07:58 |
| raitobezarius | Unnamed pairs | 21:08:07 |
 Sergei Zimmerman (xokdvium) | I did research a bit the distribution of list sizes when evaling nixpkgs. Small lists are quite often used, but lists just pale in comparison with attrsets overall | 21:17:12 |
| mzero | name value pairs are so common because of listToAttrs, etc, I wonder if a pair type would actually make a significant perf difference | 21:19:00 |
| Sergei Zimmerman (xokdvium) | A more generic approach could be to have "attrset shapes". Very similar to how v8 optimizes classes with the same layout | 21:20:09 |
| Sergei Zimmerman (xokdvium) | Then names wouldn't need to be stored in the attribute set and function calls could reuse the same memory and not copy anything to a new Env.
(I and Robert Hensing discussed this a bit at some point) | 21:21:57 |
 Qyriad | In reply to @xokdvium:matrix.org
A more generic approach could be to have "attrset shapes". Very similar to how v8 optimizes classes with the same layout benefits of a JIT especially | 21:22:04 |
| Sergei Zimmerman (xokdvium) | Not exactly tho. jit/memory layout are tangential somewhat | 21:22:32 |
| Qyriad | yeah but you can optimize hot shapes | 21:22:56 |
| Sergei Zimmerman (xokdvium) | Yeah. I think python has slots for this kind of thing | 21:23:13 |
| Sergei Zimmerman (xokdvium) | * Yeah. I think python has __slots__ for this kind of thing | 21:23:28 |
| mzero | do you have something I could read about that? I'm curious how it would work. | 21:25:02 |
| Sergei Zimmerman (xokdvium) | Probably staring at prior art in V8? I haven't done that myself, but I'd be curious how they do tracing to find hot shapes | 21:26:04 |
| Sergei Zimmerman (xokdvium) | All of those optimizations are pretty inaccessible without tracing infra :( | 21:27:26 |
| Sergei Zimmerman (xokdvium) | But tracing attrset shapes doesn't exactly depend on function call tracing. Computing a shape fingerprint and having a small hashmap of that could give a rough picture of the frequency. | 21:29:23 |
| Sergei Zimmerman (xokdvium) | So maybe only do this for attrsets smaller than N, compute a hash of symbol table ids, store it a fixed-sized map and count frequency that way. This shouldn't have much of an overhead | 21:30:50 |
| John Ericson | yeah that is in a bitrotted PR | 21:39:29 |
| 22 Nov 2025 |
 helle (just a stray cat girl) | glares at lix/nix/prefetch.cc +118 | 11:47:29 |
| helle (just a stray cat girl) | erm, why are we making a presumption there, that uh, is not actually also made by nixpkg's fetchzip (which does have stripRoot as an active choice), this with certain use cases, like what npins does, makes it impossible to compute the right hash with it | 11:48:57 |
| helle (just a stray cat girl) | (anyway, I don't think it is worth a fix, because of well, yeah) | 12:06:43 |
