Re: [PATCH/RFC] Allow writing loose objects that are corrupted in a pack file

> 
> On Wed, 7 Jan 2009, R. Tyler Ballance wrote:
> > 
> > I was only mentioning OS X with regards to the Samba/NFS red herring,
> > the rest of our operations are on 64-bit Linux machines.
> 
> Ahh, ok. Good. 
> 
> > > I could easily see that if you have a virtual memory size limit of 1.5GB, 
> > > and the pack window size is 1GB, we might have trouble. Because we could 
> > > only keep one such pack window in memory at a time.
> > 
> > The DEFAULT_PACKED_GIT_WINDOW_SIZE in our local builds is 256M, FWIW
> 
> Interesting. So you already had to lower it. However, now that you mention 
> it, and now that I search for your emails about it on the mailing list (I 
> don't normally read the mailing list except very occasionally), I see your 
> patch that does
> 
> 	#define DYNAMIC_WINDOW_SIZE_PERCENTAGE 0.85
> 	...
> 	packed_git_window_size = (unsigned int)(as->rlim_cur * DYNAMIC_WINDOW_SIZE_PERCENTAGE);
> 
> which is actually very bad.
> 
> It's bad for several reasons:
> 
>  - 85% of the virtual address space is actually pessimal.
> 
>    You need space for AT LEAST two full-sized windows, so you need less 
>    than 50%.
> 
>  - the way that variable is used, it _has_ to be a multiple of the page 
>    size. In fact, it needs to be a multiple of _twice_ the page size. So 
>    just doing a random fraction of the rlimit is not correct.

> 
> Setting it in the .gitconfig does it right, though.
> 
> > > If so, then adding a
> > > 
> > > 	[core]
> > > 		packedgitwindowsize = 64M
> > > 
> > > might make a difference. It would certainly be very interesting to hear if 
> > > there's any impact.
> > 
> > I can try this still if you'd like, but it doesn't seem like that'd be
> > the issue since we're already lowering the window size system-wide
> 
> Please do try, at least if your local git changes still match that patch I 
> found, because that patch generates problems.