PGSQL 11.4: shared_buffers and /dev/shm size

Hello,

I'm running PostgreSQL 11.4 on Linux 4.12.14 and I see the following issue while executing single one query:
ERROR: could not resize shared
memory segment "/PostgreSQL.1596105766" to 536870912 bytes: No space left on device

In my postgresql.conf I set sharred_buffers=256MB, I see that it is applied:
SHOW shared_buffers;
shared_buffers
----------------
256MB

At the same time during the query execution, I see a lot of files in /dev/shm with the total size more than 256MB

ls -lh /dev/shm
total 1.4G
-rw------- 1 postgres postgres 193K Jul 8 08:39 PostgreSQL.1026343462
-rw------- 1 postgres postgres 4.0M Jul 8 10:23 PostgreSQL.1066463809
-rw------- 1 postgres postgres 8.0M Jul 8 10:23 PostgreSQL.1154587693
-rw------- 1 postgres postgres 4.0M Jul 8 08:47 PostgreSQL.1292794952
-rw------- 1 postgres postgres 128M Jul 8 10:23 PostgreSQL.130026740
-rw------- 1 postgres postgres 8.0M Jul 8 10:23 PostgreSQL.1377271816
-rw------- 1 postgres postgres 16M Jul 8 10:23 PostgreSQL.1453162423
-rw------- 1 postgres postgres 128M Jul 8 10:23 PostgreSQL.1496397787
-rw------- 1 postgres postgres 8.0M Jul 8 10:23 PostgreSQL.1541518903
-rw------- 1 postgres postgres 64M Jul 8 10:23 PostgreSQL.1554139410
-rw------- 1 postgres postgres 2.0M Jul 8 10:23 PostgreSQL.1563273542
-rw------- 1 postgres postgres 256M Jul 8 10:23 PostgreSQL.1604524364
-rw------- 1 postgres postgres 64M Jul 8 10:23 PostgreSQL.1624127960
-rw------- 1 postgres postgres 4.0M Jul 8 10:23 PostgreSQL.1674892421
-rw------- 1 postgres postgres 128M Jul 8 10:32 PostgreSQL.179085785
-rw------- 1 postgres postgres 32M Jul 8 10:23 PostgreSQL.1921401343
-rw------- 1 postgres postgres 32M Jul 8 10:23 PostgreSQL.1931571650
-rw------- 1 postgres postgres 2.0M Jul 8 10:23 PostgreSQL.2002232858
-rw------- 1 postgres postgres 2.0M Jul 8 10:23 PostgreSQL.2057901523
-rw------- 1 postgres postgres 2.0M Jul 8 10:23 PostgreSQL.2110310896
-rw------- 1 postgres postgres 65M Jul 8 08:39 PostgreSQL.2136390898
-rw------- 1 postgres postgres 182K Jul 8 08:39 PostgreSQL.261370809
-rw------- 1 postgres postgres 16M Jul 8 10:23 PostgreSQL.397419407
-rw------- 1 postgres postgres 4.0M Jul 8 10:23 PostgreSQL.431734656
-rw------- 1 postgres postgres 128M Jul 8 10:23 PostgreSQL.478359814
-rw------- 1 postgres postgres 8.0M Jul 8 10:23 PostgreSQL.489042863
-rw------- 1 postgres postgres 64M Jul 8 10:23 PostgreSQL.590987495
-rw------- 1 postgres postgres 3.4M Jul 8 08:39 PostgreSQL.62466476
-rw------- 1 postgres postgres 16M Jul 8 10:23 PostgreSQL.629400316
-rw------- 1 postgres postgres 6.8K Jul 8 08:39 PostgreSQL.741718396
-rw------- 1 postgres postgres 16M Jul 8 10:23 PostgreSQL.770970033
-rw------- 1 postgres postgres 1.0M Jul 8 10:23 PostgreSQL.776045115
-rw------- 1 postgres postgres 64M Jul 8 10:23 PostgreSQL.795742467
-rw------- 1 postgres postgres 32M Jul 8 10:23 PostgreSQL.835134775
-rw------- 1 postgres postgres 32M Jul 8 10:23 PostgreSQL.953710812

How can I configure limit for total shared memory size?

Best regards,
Konstantin