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

[Mike Hommey <mh@glandium.org>]

On Thu, Jul 04, 2019 at 12:04:11PM +0000, Eric Wong wrote:
> Mike Hommey <mh@glandium.org> wrote:
> > I'm puzzled by the fact writing objects is so much faster with 1 thread.
> 
> I/O contention in the multi-threaded cases?
> 
> "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.
 
> As for memory use, does git use the producer/consumer pattern
> for malloc+free so free happens in a different thread from the
> malloc?
> 
> Because current versions of glibc gets pathological with that case
> (but I have a long-term fix for it):
> 
> https://public-inbox.org/libc-alpha/20180731084936.g4yw6wnvt677miti@dcvr/T/
> Only locklessinc malloc seemed OK in the IPC department
> (But I haven't kept up with jemalloc, tcmalloc developments in years)

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.

Mike

1. https://sourceware.org/bugzilla/show_bug.cgi?id=23416