Patches to reduce GFS2 fragmentation

Hi,

This is a revised version of my patches to improve GFS2 performance and reduce GFS2 fragmentation. As suggested by Steve Whitehouse, the first patch has been modified to base its distribution of resource groups on the number of journals. It also corrects the criteria on the final loop, changing "loops < 3" back to "loops < 2" as it should be. Also, I re-tested to make sure nothing had regressed. I updated the timing numbers below.

Also as suggested, the patch that kept file close from deleting rgrp reservations has been removed from the set, leaving only three patches. The removal of that patch caused fragmentation to climb 15 percent, but it's still much (41 percent) better than the original stock kernels. I agree that use cases like untar would make for much worse fragmentation problems if that patch were to remain.

I've re-tested with these three patches and found that performance and fragmentation are still good. Here are numbers:

STOCK RHEL7 kernel (none of these patches):

Run times:
Run 1 time: 2hr 40min 33sec
Run 2 time: 2hr 39min 52sec
Run 3 time: 2hr 39min 31sec
Run 4 time: 2hr 33min 57sec
Run 5 time: 2hr 41min 6sec

Total file extents (File fragmentation):

EXTENT COUNT FOR OUTPUT FILES =  744708
EXTENT COUNT FOR OUTPUT FILES =  749868
EXTENT COUNT FOR OUTPUT FILES =  721862
EXTENT COUNT FOR OUTPUT FILES =  635301
EXTENT COUNT FOR OUTPUT FILES =  689263

The times are bad and the fragmentation level is also bad. If I add just the first patch, "GFS2: Set of distributed preferences for rgrps" the performance improves, but the fragmentation is worse (I only did three iterations this time):

Run times:
Run 1 time: 2hr 2min 47sec
Run 2 time: 2hr 8min 37sec
Run 3 time: 2hr 10min 0sec

Total file extents (File fragmentation):

EXTENT COUNT FOR OUTPUT FILES =  1011217
EXTENT COUNT FOR OUTPUT FILES =  1025973
EXTENT COUNT FOR OUTPUT FILES =  1070163

With these three patches, both performance and fragmentation are good:

Run 1 time: 2hr 11min 11sec
Run 2 time: 2hr 8min 57sec
Run 3 time: 2hr 10min 43sec
Run 4 time: 2hr 12min 50sec
Run 5 time: 2hr 15min 32sec
Run 6 time: 2hr 10min 58sec

EXTENT COUNT FOR OUTPUT FILES =  424329
EXTENT COUNT FOR OUTPUT FILES =  430663
EXTENT COUNT FOR OUTPUT FILES =  430186
EXTENT COUNT FOR OUTPUT FILES =  421635
EXTENT COUNT FOR OUTPUT FILES =  416706
EXTENT COUNT FOR OUTPUT FILES =  418887

Regards,

Bob Peterson
Red Hat File Systems

---
Bob Peterson (3):
GFS2: Set of distributed preferences for rgrps
GFS2: Only increase rs_sizehint
GFS2: If we use up our block reservation, request more next time

 fs/gfs2/file.c   |  3 ++-
 fs/gfs2/incore.h |  1 +
 fs/gfs2/rgrp.c   | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
 fs/gfs2/rgrp.h   |  1 +
 4 files changed, 68 insertions(+), 6 deletions(-)

1.9.3