Hi,
today I tried the wip-librbd-caching branch. The performance improvement
is very good particular for small writes.
I tested from within a vm with fio:
rbd_cache_enabled=1
fio -name iops -rw=write -size=10G -iodepth 1 -filename /tmp/bigfile
-ioengine libaio -direct 1 -bs 4k
I get over 10k iops
With an iodepth 4 I get over 30k iops
In comparison with the rbd_writebackwindow I get around 5k iops with an
iodepth of 1.
So far the whole cluster is running stable for over 12 hours.
But there is also a downside.
My typical vm are 1Gb in size, the default cache size is 200Mb, which is
20% more memory usage. Maybe 50Mb or less will be enough?
I am going to test that.
The other point is, that the cache is not KSM enabled, therefore
identical pages will not be merged, could that be changed, what would be
the downside?
So maybe we could reduce the memory footprint of the cache, but keep
it's performance.
-martin
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