From: Linus Torvalds Date: Fri, 07 Oct 2005 15:34:19 GMT Subject: Re: First cut at git port to Cygwin Message-ID: In-Reply-To: <81b0412b0510070544v3e7cf0b4n521db8ff7e4e335a@mail.gmail.com> On Fri, 7 Oct 2005, Alex Riesen wrote: > > it suddenly get worse: now I'm stuck on git-pull. > > git-merge-index (called at some point by git-pull) maps the index in, and starts > git-merge-one-file for each (or the given) entry in the index. > git-merge-one-file > calls git-update-index, which wants to update the index. Which doesn't work, > because it's locked by that piece of s$%^. NOTE! git doesn't use mmap() because it _needs_ to use mmap(), but because it was simple to do that way, and it's a total idiosyncracy of mine that I often try to mmap the data. I often also tend to do my own allocators instead of using malloc() (see my "sparse" project in case you're interested in other idiosyncracies of mine - macros to do list traversal etc). The fact is, "mmap()" isn't really any better than "read()": it has some advantages wrt memory management for the kernel, which is probably one big reason why I do it, but quite frankly, if you were to change every single mmap() to be a "map_file()" instead, and made it optional whether it used mmap() or "malloc + read()", I personally don't think it would be horrible. And it might make things much simpler for portability. The "use mmap" approach is very much a unixism, particularly the way unix people do it (mmap followed by close, making the file descriptor "go away"). Sure, other OS's have mmap too, but I think on them it tends to be less commonly used. Linus