5 ms·

I was expecting this statement to be expounded: > Unfortunately this meant some of the performance wins needed to be sacrificed to avoid an increased memory fo

• loeg 3y ago
  I think the idea is they might reduce the alignment in places to save memory.
  • wongarsu 3y ago
    In case anyone wants to try the same, my assumption is that they specified `#[repr(packed(8))]` on some structs to use alignments and paddings of at most 8 bytes. Using `[repr(align(8))]` on the field should also work, if you want more fine-grained control. https://doc.rust-lang.org/reference/type-layout.html#the-alignment-modifiers https://doc.rust-lang.org/reference/type-layout.html#the-ali...
    • thayne 3y ago
      > my assumption is that they specified `#[repr(packed(8))]` on some structs to use alignments and paddings of at most 8 bytes That would mean taking a reference of any field of that struct is undefined behavior, unless the compiler does some special magic for this specific case. > Using `[repr(align(8))]` on the field I don't think you can do that directly. You would need to use a newtype that specified the alignment, and use that type for the field.
  • thayne 3y ago
    That would make sense, but I would like to know in which situations that happens. And can I manually reduce the alignment in a struct (say to an alignment of 8 with a struct that has other fields with alignment of 8) to reduce memory usage? Or ensure that a location uses an alignment of 16 in places I want the higher performance.