From: Junio C Hamano <gitster@pobox.com>
Date: Sun, 22 Nov 2020 20:32:01 GMT
Subject: Re: [PATCH 07/23] ewah: make bitmap growth less aggressive
Message-ID: <xmqq7dqdqgji.fsf@gitster.c.googlers.com>
In-Reply-To: <c7db594fae4d0447a55a92e830475d9bc418ae7f.1605123652.git.me@ttaylorr.com>

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)?

Thanks.