[fpc-devel] Unit loading overhead

Jonas Maebe jonas.maebe at elis.ugent.be
Tue Jul 20 13:00:59 CEST 2010

On 17 Jul 2010, at 21:50, Micha Nelissen wrote:

> Jonas Maebe wrote:
>> All applications but the ones that allocate a only few memory blocks (especially in case it's a few small blocks of many different sizes) would benefit from this change, not just apps allocating hundreds of megabytes at the same time (it also helps in case applications maximally use 10MB, but allocate and free a lot of data so the blocks get released back to the OS). Applications allocating a ton of them would obviously benefit more than others.
> So why 256kb? not 64, 128, or 512kb?

I've now committed a dynamic scheme that starts of with chunks of 32KiB, but which grows the chunk size (per thread) as more and more get allocated (up to a limit of 256KiB). The speed is only slightly lower than when starting of immediately with 256KiB blocks, and for apps performing only a few allocations nothing changes regarding the amount of memory they use.

The 256KiB upper limit comes from benchmarking the compiler both when compiling itself (average scenario, mixed allocations and frees) and the "all packages units" (extreme scenario). Going higher did not provide noticeable speed gains while increasing memory usage quite a bit. The same goes for the limit of when the size of the chunks to allocate is doubled.


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