On 2016-10-14 02:28, Stefan Priebe - Profihost AG wrote:
Hello list,
while running the same workload on two machines (single xeon and a dual
xeon) both with 64GB RAM.
I need to run echo 3 >/proc/sys/vm/drop_caches every 15-30 minutes to
keep the speed as good as on the non numa system. I'm not sure whether
this is related to numa.
Is there any sysctl parameter to tune?
Tested with vanilla v4.8.1
This may sound odd, but does echoing 1 or 2 to /proc/sys/vm/drop_caches
help at all, or is it just 3? The value itself is actually a bit-field
with just two bits defined. 1 just drops the page-cache, while 2 just
drops freeable SLAB objects, and 3 drops both. The thing is, both have
an impact when dealing with filesystems (page-cache contains cached file
contents, while freeable SLAB objects includes cached dentries and
inodes), so knowing whether one or the other or only both is what's
helping things can help diagnose this further.
Regardless of that, you might try adjusting vm.vfs_cache_pressure.
Increasing that will make the page-cache reclaim more aggressive, while
decreasing it will make it less aggressive. It defaults to 100, and I
wouldn't suggest setting it below 50 or above about 150. Keep in mind
that increasing that will mean you're likely to put more load on the
storage devices.
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