Comment 2 for bug 1416582

My bad, Agustin. Able to reproduce the same while using log file name without .log extension.
For using max_slowlog_size, as per the Doc,
"Warning For this feature to work variable slow_query_log_file needs to be set up manually and without the .log sufix. The slow query log files will be named using slow_query_log_file as a stem, to which a dot and a sequence number will be appended."
http://www.percona.com/doc/percona-server/5.6/flexibility/slowlog_rotation.html

root@desktop:/var/lib/mysql# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 37
Server version: 5.6.22-71.0-log Percona Server (GPL), Release 71.0, Revision 726

Copyright (c) 2009-2014 Percona LLC and/or its affiliates
Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show variables like '%version%';
+-------------------------+--------------------------------------------------+
| Variable_name | Value |
+-------------------------+--------------------------------------------------+
| innodb_version | 5.6.22-71.0 |
| protocol_version | 10 |
| slave_type_conversions | |
| version | 5.6.22-71.0-log |
| version_comment | Percona Server (GPL), Release 71.0, Revision 726 |
| version_compile_machine | x86_64 |
| version_compile_os | debian-linux-gnu |
+-------------------------+--------------------------------------------------+
7 rows in set (0.00 sec)

mysql> show variables like 'max_slowlog_%';
+-------------------+-------+
| Variable_name | Value |
+-------------------+-------+
| max_slowlog_files | 0 |
| max_slowlog_size | 8192 |
+-------------------+-------+
2 rows in set (0.00 sec)

mysql> show variables like 'slow_query_log%';
+------------------------------------+---------------------------------+
| Variable_name | Value |
+------------------------------------+---------------------------------+
| slow_query_log | ON |
| slow_query_log_always_write_time | 10.000000 |
| slow_query_log_file | /var/lib/mysql/desktop-slow-log |
| slow_query_log_timestamp_always | OFF |
| slow_query_log_timestamp_precision | second |
| slow_query_log_use_global_control | |
+------------------------------------+---------------------------------+
6 rows in set (0.00 sec)

mysql> set global slow_query_log=0;
Query OK, 0 rows affected (0.00 sec)

mysql> set global slow_query_log=1;
Query OK, 0 rows affected (0.00 sec)

mysql> set global slow_query_log=0;
Query OK, 0 rows affected (0.00 sec)

mysql> set global slow_query_log=1;
Query OK, 0 rows affected (0.00 sec)

mysql>
root@desktop:/var/lib/mysql# ll
total 307472
drwx------ 6 mysql mysql 4096 Feb 3 12:47 ./
drwxr-xr-x 72 root root 4096 Feb 1 20:09 ../
-rw-rw---- 1 mysql mysql 56 Jan 16 14:59 auto.cnf
-rw-r--r-- 1 root root 0 Jan 16 14:59 debian-5.6.flag
-rw-r----- 1 mysql root 82017 Jan 27 13:29 desktop.err
-rw-rw---- 1 mysql mysql 5 Feb 3 12:46 desktop.pid
-rw-rw---- 1 mysql mysql 186 Feb 3 12:46 desktop-slow-log.000001
-rw-rw---- 1 mysql mysql 210 Feb 3 12:47 desktop-slow-log.000002
-rw-rw---- 1 mysql mysql 210 Feb 3 12:47 desktop-slow-log.000003
-rw-r----- 1 mysql root 131967 Feb 3 12:46 error.log
-rw-rw---- 1 mysql mysql 213909504 Feb 3 12:46 ibdata1
-rw-rw---- 1 mysql mysql 50331648 Feb 3 12:46 ib_logfile0
-rw-rw---- 1 mysql mysql 50331648 Feb 3 12:46 ib_logfile1
drwx------ 2 mysql mysql 4096 Jan 16 14:59 mysql/
-rw------- 1 root root 11 Jan 16 14:59 mysql_upgrade_info
dr-x------ 2 mysql mysql 4096 Jan 27 13:30 nil/
drwx------ 2 mysql mysql 4096 Jan 16 14:59 performance_schema/
drwx------ 2 mysql mysql 4096 Jan 16 14:59 test/
root@desktop:/var/lib/mysql#