Git server memory requirements

I'm trying to get an idea how much memory is required for a git server that is hosting linux kernel repos.

What we're seeing is that git uses around 1GB of RAM on the server when a user does a clone of the Linux kernel source over ssh. Does this seem about right? Is this amount fixed, or arbitrary (trade-off memory for speed). It seems subsequent concurrent clones use less memory.

Is there any practical way to reduce the memory usage? We're running into occasional issues if there are multiple clones at once.

Is setting gc.auto=0 a good idea for large kernel repos? The idea is we can repack manually or in a cron on weekends rather than during user operations. However, manually running a git gc seems to use about as much memory as a user clone.

It may be that our EC2 small instance (2.5GB) is not up to the task, but would like to understand options (we can easily trade off some speed for less memory if we can) before upgrading.

Thanks, Cliff