[dm-devel] [PATCH v3 0/5] multipath: optimizations for large mptable

[mwilck at suse.com]

From: Martin Wilck <mwilck at suse.com>

We observe that multipath operations take a long time if the multipaths
section in multipath.conf contains a lot of alias settings
(10000+ in our case). This hurts in particular in udev rules, when
multipath -u or multipath -U is invoked, but also for command line
invocations like "multipath -ll".

This series provides a few optimizations for this use case. It speeds
up simple multipath operations in the test case by a factor of 20.

Changes v2->v3, after discussion with Benjamin Marzinski:

 01, 02: added msort.c from glibc and adapted to our needs.
         Numbering changes accordingly.
 03, 04: (was 01, 02): remove pointer comparisons from v2 again, this was a
         dumb idea. Use the stable msort algorithm instead.

Changes wrt v1, after suggestions from Benjamin Marzinski:

 01, 02: Use pointer comparisons to achieve stable sorting with qsort
 02:  Fix return without popping the cleanup handler. The way I fixed this
      leaves the possibility that some memory won't be freed if a thread is
      killed while executing vector_convert(). I think this is acceptible;
      avoiding it would complicate the code, with very small benefit.
 02: Remove unnecessary checks and break loop if alias==NULL is encountered.

Martin Wilck (5):
  libmultipath: add msort.c from glibc
  libmultipath: modifications for msort.c
  libmultipath: merge_mptable(): sort table by wwid
  libmultipath: check_alias_settings(): pre-sort mptable by alias
  multipath: optimize program startup for frequent invocations

 libmultipath/Makefile |   2 +-
 libmultipath/alias.c  |  37 +++++-
 libmultipath/config.c |  15 ++-
 libmultipath/msort.c  | 268 ++++++++++++++++++++++++++++++++++++++++++
 libmultipath/msort.h  |   6 +
 libmultipath/vector.c |   9 ++
 libmultipath/vector.h |   1 +
 multipath/main.c      |  33 +++---
 8 files changed, 349 insertions(+), 22 deletions(-)
 create mode 100644 libmultipath/msort.c
 create mode 100644 libmultipath/msort.h

-- 
2.37.1