> From: Lynn Winebarger <owinebar@gmail.com>
> Not that I don't enjoy trawling through old threads in the emacs-devel archive
> (searching for mmap led to a thread from the introduction of the portable dumper),
> but it would be a lot easier if there were design notes somewhere recording
> the rationale of the decisions reflected in the current code.
We lack someone in the role of the "project historian", who would then
summarize and publish the design discussions in the form of such
notes. Volunteers are most welcome.
It's not the discussion (or history) per se, but the factors that decided the current
design choices. An example would be the #ifdef DOUG_LEA_MALLOC blocks in lisp_align_malloc
of alloc.c that prevent allocating via mmap. So far what I've read indicates
that step is there to enable dumping by unexec (assuming I've understood correctly).
Ideally there would be a design note (possibly generated from comments, possibly free standing)
that would explain what the purpose of the restriction is, so you could tell if it's still
relevant, and any negative impacts it has. Also, if there are plans to remove it at
some point, what (if any) the requirements/test for removing it would be, etc. By "it",
I mean any hypothetical design point, not just this particular one.
Alternative designs could also be discussed along with the factors that led
to their rejection, if it was significant enough.
Now, those could be derived from mailing list discussions, but I wouldn't consider them
"history". Per subsequent mails in this thread, if a developer or code reviewer made
a practice of citing particular mail messages (or even other sources), some extraction
process might even be automated, but then there would be the question of copyright
assignment. It would help if there were some taxonomy of features/design points for
reference. Is the bug database being used for that?
Actually, a good example (even though it's more post facto description than prospective
That is really useful documentation that would ideally be in the emacs docs or etc directory.
Andrea's development log and paper on the compiler are another example.
The development log would benefit (in terms of use as design notes) from de-chronologizing
them, figuring out the right taxonomy of the various topics, and gathering the material accordingly.
I put in a request to
assign@gnu.org a few days ago, but I have not received any response yet.
> The best I can do now
> is comb through the arguments on the list (and maybe in the bug tracker?) and
> try to guess which points ended up getting reflected in the code.
A better method is to use Git logs to find when the GNU/Linux build
stopped using mmap, and then search the archives around that time.
> I will say jemalloc appears to have a lot of heap profiling bells and whistles.
AFAIU, so does glibc. Some of them where mentioned in the discussions
you already unearthed, AFAIR.
I figured it would. jemalloc's maintainers just spend a lot of effort highlighting those features in the
documentation. I wouldn't be surprised if it was 3/4 of the material on the package's site
is dedicated to how to use jemalloc's profiling for debugging or optimizing
memory allocation in the calling program. It makes an impression.
Lynn