YJIT: Pack BlockId and CodePtr #6748
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XrXr
reviewed
Nov 16, 2022
| @@ -59,7 +59,7 @@ pub trait Allocator { | |||
| /// We may later change this to wrap an u32. | |||
| /// Note: there is no NULL constant for CodePtr. You should use Option<CodePtr> instead. | |||
| #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Debug)] | |||
| #[repr(C)] | |||
| #[repr(C, packed)] | |||
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I'm curious how much this change to CodePtr alone affects things. This doesn't change the size but allows the pointer to be stored unaligned: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=6f40323dcc2d2898fb01d2309d734102
Maybe the compiler sees this and gives struct Block a more compact layout?
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It has a relatively big impact for some reason.
With CodePtr not packed
code_region_size: 9715712
yjit_alloc_size: 19684821
With CodePtr packed
code_region_size: 9715712
yjit_alloc_size: 18179277
XrXr
approved these changes
Nov 16, 2022
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This reduces memory usage on railsbench from 20.9MB to 18.2MB.
Before
After