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(author) > A very well thought out set of functionality Thanks! It's only an experiment at this stage but I was pleasantly surprised it worked in such a smal

(author) > A very well thought out set of functionality Thanks! It's only an experiment at this stage but I was pleasantly surprised it worked in such a small size. > slices (...) generally faster It works wonders. The upcoming bft_split function is gonna be dead fast. I optimize things by adopting the laziest possible personna : do I really need to copy this ? No. What if the user wants to append stuff to a split part ? We'll see then. > Allocating only blocks sized by a power of two is potentially memory wasting It just follows the classical doubling of requested size. In high exponents though I admit it'll be wasteful. > some clever base between 1 and 2 I wouldn't have thought of it, nor known how to. Would it be somehow costly ? Shifting is basically free. > support 'mmap' Interesting. But shouldn't we keep the lib surface minimal and just leave this to the user ? She maps then takes a view on it ?

samatman 5y ago
Hey, an opportunity to shill my favorite ISO standard! It's 3. ISO 3, preferred numbers: https://en.wikipedia.org/wiki/Preferred_number#Computer_engineering https://en.wikipedia.org/wiki/Preferred_number#Computer_engi... For your application, I would apply a heuristic which includes the x3 values at some point (256KiB?), and maybe the x5 values near/at 256MiB. Allocation is so expensive relative to calculating the allocated value that you could use something really complex and it would work. Certainly multiplying by a factor between one and two and rounding to the nearest word would work, there's no way you'd see a performance difference from the calculation. The advantage of ISO 3 is that the user always gets a familiar number of allocated bytes back.
newaccount74 5y ago
> > some clever base between 1 and 2 > I wouldn't have thought of it, nor known how to. Would it be somehow costly ? Shifting is basically free. Multiplying by 1.5 is a shift and an add, so just as cheap. Multiplying by 1.5 has the advantage that 1 + 1.5 > 1.5 * 1.5, so the second time you realloc it fits into the old memory (which can help reduce memory fragmentation if the allocator takes advantage of it).
- stephencanon 5y ago
  > Multiplying by 1.5 has the advantage that 1 + 1.5 > 1.5 * 1.5, so the second time you realloc it fits into the old memory (which can help reduce memory fragmentation if the allocator takes advantage of it). I’m really struggling to think of any mainstream allocator that can take advantage of this.
- rurban 5y ago
  The clever base between 1 and 2 you are looking for is the golden ratio. I would use it only for bigger numbers though. under 5k 2 is good enough.

samatman 5y ago

Hey, an opportunity to shill my favorite ISO standard! It's 3. ISO 3, preferred numbers: https://en.wikipedia.org/wiki/Preferred_number#Computer_engineering https://en.wikipedia.org/wiki/Preferred_number#Computer_engi... For your application, I would apply a heuristic which includes the x3 values at some point (256KiB?), and maybe the x5 values near/at 256MiB. Allocation is so expensive relative to calculating the allocated value that you could use something really complex and it would work. Certainly multiplying by a factor between one and two and rounding to the nearest word would work, there's no way you'd see a performance difference from the calculation. The advantage of ISO 3 is that the user always gets a familiar number of allocated bytes back.

newaccount74 5y ago

> > some clever base between 1 and 2 > I wouldn't have thought of it, nor known how to. Would it be somehow costly ? Shifting is basically free. Multiplying by 1.5 is a shift and an add, so just as cheap. Multiplying by 1.5 has the advantage that 1 + 1.5 > 1.5 * 1.5, so the second time you realloc it fits into the old memory (which can help reduce memory fragmentation if the allocator takes advantage of it).

stephencanon 5y ago
> Multiplying by 1.5 has the advantage that 1 + 1.5 > 1.5 * 1.5, so the second time you realloc it fits into the old memory (which can help reduce memory fragmentation if the allocator takes advantage of it). I’m really struggling to think of any mainstream allocator that can take advantage of this.
rurban 5y ago
The clever base between 1 and 2 you are looking for is the golden ratio. I would use it only for bigger numbers though. under 5k 2 is good enough.