Problem:
Server throws OOM error when we execute twitter load with SELECTs
for UPDATE + UPDATES, and SELECT queries on tables with full-text
index.
FTS cache->total_memory store count of total memory allocated to FTS
cache (for all fulltext indexes on a table).
For each word in fts cache, we store doc-id & word position in a
node->ilist.
we increment cache->total_memory with size of doc-id & word position
whereas we allocate ilist in chuck of 16, 32 ,64 bytes or 1.2 times
of last size.
When we wil insert huge amount of data into the FTS aux index tables
then collectively these small chucks for each token become huge
unaccounted memory allocated for FTS cache.

Fix:
Incremented cache->total_memory by size of chunk allocated to
node->ilist.

RB: 25286
Reviewed by : Rahul Agarkar <rahul.agarkar@oracle.com>

mysql/mysql-server@7ab5707f1c4482ed050ed9fa739e9ec0e2fc0ffa