Blocked updates and background writer performance

PG 9.4.4 (RDS)

I'm experiencing an issue when trying to update many rows in a single table
(one row at a time, but parallelized across ~12 connections). The issue we
see is that the writes will periodically be blocked for a duration of
several minutes and then pick back up. After digging through our
monitoring stack, I was able to uncover these stats which seem to allude to
it being a background writer performance problem:

[image: bg_writer.png]
(apologies for the image)

Our settings for the background writer are pretty standard OOB (I threw in
some others that I thought might be helpful, too):

name | setting | unit
-------------------------+---------+------
bgwriter_delay | 200 | ms
bgwriter_lru_maxpages | 100 |
bgwriter_lru_multiplier | 2 |
maintenance_work_mem | 65536 | kB
max_worker_processes | 8 |
work_mem | 32768 | kB

The table that is being written to contains a jsonb column with a GIN index:

Table "public.ced"
Column | Type | Modifiers
---------------+--------------------------+-----------
id | bigint | not null
created_at | timestamp with time zone |
modified_at | timestamp with time zone |
bean_version | bigint | default 0
account_id | bigint | not null
data | jsonb | not null
Indexes:
"ced_pkey" PRIMARY KEY, btree (id)
"ced_data" gin (data jsonb_path_ops)
"partition_key_idx" btree (account_id, id)

It seems to me that the background writer just can't keep up with the
amount of writes that I am trying to do and freezes all the updates. What
are my options to improve the background writer performance here?

thanks
--Cory