Re: git-daemon on NSLU2

[Linus Torvalds <torvalds@linux-foundation.org>]

On Fri, 24 Aug 2007, Jon Smirl wrote:
> 
> We're going something wrong in git-daemon.

Nope.

Or rather, it's mostly by design.

> I can clone the tree in five minutes using the http protocol. Using the 
> git protocol would take 24hrs if I let it finish.

The http side doesn't actually do any global verification, the way 
git-daemon does. So to it, everything is just temporary buffers, and you 
don't need any memory at all, really.

git-daemon will create a packfile. That means that it has to generate the 
*global* object reachability, and will then optimize the object packing 
etc etc. That's a minimum of something like 48 bytes per object for just 
the object chains, and the kernel has a *lot* of objects (over half a 
million).

In addition to the object chains yourself, the native protocol will also 
obviously have to actually *look* at and parse all the tree and commit 
objects while it does all this, so while it doesn't necessarily keep all 
of those in memory all the time, it will need to access them, and if you 
don't have enough memory to cache them, that will add its own set of IO.

So I haven't checked exactly how much memory you really want to have to 
serve big projects, but with some handwavy guesstimate, if you actually 
want to do a good job I'd guess that you really want to have at least as 
much memory as the size of largest project you are serving, and probably 
add at least 10-20% on top of that.

So for the kernel, at a guess, you'd probably want to have at least 256MB 
of RAM to do a half-way good job. 512MB is likely nicer and allows you to 
actually cache the stuff over multiple accesses.

But I haven't actually tested. Maybe it might be bearable at 128M.

			Linus