Re: Surprising use of memory and time when repacking mozilla's gecko repository

> On Thu, Jul 04, 2019 at 10:13:20PM +0900, Mike Hommey wrote:
> 
> > > "public-inbox-index" (reading from git, writing to Xapian+SQLite)
> > > on a dev machine got slow because core count exceeded what SATA
> > > could handle and had to cap the default Xapian shard count to 3
> > > by default for v2 inboxes.
> >  
> > AFAICT, git doesn't write from multiple threads.
> 
> Right. That's always single threaded, and the main difference there is
> going to be what's in the delta base cache.
> 
> > Oh right, I forgot to mention:
> > - I thought this memory usage thing was [1] but it turns out it was real
> >   memory usage.
> > - glibc's mallinfo stores values as int, so it's useless to know how
> >   much memory was allocated when it's more than 4GB.
> > - glibc's malloc_stats relies on the same int data, so while it does
> >   print "in use" data, it can't print values above 4GB correctly.
> > - glibc has a malloc_stats function that, according to its manual page
> >   "addresses the deficiencies in malloc_stats and mallinfo", but while
> >   it outputs a large XML dump, it doesn't contain anything that looks
> >   remotely like the "in use" from malloc_stats.
> > - So all in all, I used jemalloc to gather the "allocated" stats.
> 
> I think I explained all of the memory-usage questions in my earlier
> response, but just for reference: if you have access to it, valgrind's
> "massif" tool is really good for this kind of profiling. Something like:
> 
>   valgrind --tool=massif git pack-objects ...
>   ms_print massif.out.*
> 
> which shows heap usage at various times, points out the snapshot with
> peak usage, and shows a backtrace of the main culprits at a few
> snapshots.