Re: Cygwin can't handle huge packfiles?

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Apr 3, 2006, 15:12 UTC
Message-ID: <Pine.LNX.4.63.0604031710440.9360@wbgn013.biozentrum.uni-wuerzburg.de>
In-Reply-To: <Pine.LNX.4.64.0604030730040.3781@g5.osdl.org>

Hi,

On Mon, 3 Apr 2006, Linus Torvalds wrote:

Show 14 quoted lines

> On Mon, 3 Apr 2006, Johannes Schindelin wrote:
> > 
> > The problem is not mmap() on cygwin, but that a fork() has to jump through 
> > loops to reinstall the open file descriptors on cygwin. If the 
> > corresponding file was deleted, that fails. Therefore, we work around that 
> > on cygwin by actually reading the file into memory, *not* mmap()ing it.
> 
> Well, we could actually do a _real_ mmap on pack-files. The pack-files are 
> much better mmap'ed - there we don't _want_ them to be removed while we're 
> using them. It was the index file etc that was problematic.
> 
> Maybe the cygwin fake mmap should be triggered only for the index (and 
> possibly the individual objects - if only because there doing a 
> malloc+read may actually be faster).

I hit the problem *only* with "git-whatchanged -p". Which means that the upcoming we-no-longer-write-temp-files-for-diff version should make that gitfakemmap() hack obsolete. (I have not checked whether there are other places where a file is mmap()ed and then used by a fork()ed process.)

Ciao, Dscho