Memory usage of the machine with ES is continuously increasing

Elastic Stack Elasticsearch
10

I have straced elasticsearch for a couple of minutes
strace -fp PID -o file.txt

out of the 40k+ events recorded
2.2k + events have resulted in errors like this

I think this is the reason for the dentry bloating, though I am not sure if
there is some thing wrong with my cluster or not.

On Monday, May 4, 2015 at 4:17:40 PM UTC+5:30, Pradeep Reddy wrote:

ES version 1.5.2
Arch Linux on Amazon EC2
of the available 16 GB, 8 GB is heap (mlocked). Memory consumption is
continuously increasing (225 MB per day).
Total no of documents is around 800k, 500 MB.

cat /proc/meminfo has

Slab: 3424728 kB

SReclaimable: 3407256 kB

curl -XGET 'http://localhost:9200/_nodes/stats/jvm?pretty'

"heap_used_in_bytes" : 5788779888,
"heap_used_percent" : 67,
"heap_committed_in_bytes" : 8555069440,

slabtop
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE
NAME
17750313 17750313 100% 0.19K 845253 21 3381012K dentry

So the continuous increase in memory usage is because of the slab usage I
think, If I restart ES, then slab memory is freed. I see that ES still has
some free heap available, but from elastic documentation

Lucene is designed to leverage the underlying OS for caching in-memory
data structures. Lucene segments are stored in individual files. Because
segments are immutable, these files never change. This makes them very
cache friendly, and the underlying OS will happily keep hot segments
resident in memory for faster access.

My question is, should I add more nodes or increase the ram of each node
to let lucene use as much memory as it wants ? how significant performance
difference will be there if I choose to upgrade ES machines to have more
RAM.

Or, can I make some optimizations that decreases the slab usage or clean
slab memory partially?

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