Re: [PATCH 0/17] Sliding window mmap for packfiles.

From: Shawn Pearce <spearce@spearce.org>
Date: Dec 24, 2006, 09:05 UTC
Message-ID: <20061224090508.GF7443@spearce.org>
In-Reply-To: <38b2ab8a0612240056k152344ael891e9b0b9f8cbc47@mail.gmail.com>

Francis Moreau <francis.moro@gmail.com> wrote:

Show 11 quoted lines

> On 12/23/06, Shawn O. Pearce <spearce@spearce.org> wrote:
> >This 17 patch series implements my much discussed, but never produced
> [snip]
> >
> >This series also permits accessing packfiles up to 4 GiB in size,
> >even on systems which permit only 2 GiB of virtual memory within
> >a single process (e.g. Windows and some older UNIXes).  Of course
> 
> Just out of curiosity, do you mean that there are some OS running on
> 32 bits machines which allow 4GiB size of virtual memory within a
> single process ? If so, could you give an example of such OS ?

No. What I meant was the Git packfile/index format currently supports up to 4 GiB of data in a single packfile. But *no* OS using 32 bit virtual address space would permit us to access that packfile prior to this series as we would have *no* memory left for a stack, let alone for parsing commits, etc., as *all* of the address space would have been dedicated to the packfile.

However with this series even a 32 bit OS which only permits processes to have at most 2 GiB of address space (2 GiB split between kernel space and userspace) can access packfiles up to 4 GiB in size. That seems to be the split most OSes wind up using, if they didn't push it out to 3.2 GiB like Linux and Solaris have done.

This series is a good change because Git can now really make full use of the space allowed by a single packfile. :-)

-- 
Shawn.