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> On Mon, Nov 23, 2020 at 11:49:49AM -0500, Taylor Blau wrote:
>
>> On Sun, Nov 22, 2020 at 12:32:01PM -0800, Junio C Hamano wrote:
>> > Taylor Blau <me@ttaylorr.com> writes:
>> >
>> > > - a geometric increase in existing size; we'll switch to 3/2 instead of
>> > > 2 here. That's less aggressive and may help avoid fragmenting memory
>> > > (N + 3N/2 > 9N/4, so old chunks can be reused as we scale up).
>> >
>> > I am sure this is something obvious to bitmap folks, but where does
>> > 9N/4 come from (I get that the left-hand-side of the comparison is
>> > the memory necessary to hold both the old and the new copy while
>> > reallocating the words[] array)?
>>
>> I thought that I was in the group of "bitmap folks", but since it's not
>> obvious to me either, I guess I'll have to hand in my bitmap folks
>> membership card ;).
>>
>> Peff: where does 9N/4 come from?
>
> it is not a bitmap thing at all. We are growing a buffer, so if we
> continually multiply it by 3/2, then our sequence of sizes is:
>
> - before growth: N
> - after 1 growth: 3N/2
> - after 2 growths: 9N/4
Junio C Hamano <gitster@pobox.com>