Why mysqld binary file size auto change

[daiguadaidai]

OS: Centos6.5
MySQL 5.6.37
at first use mysql binary tar ball mysqld file size is same。but running with 3 day。mysqld size is change:
3 day ago:

find / -name mysqld | xargs ls -la
-rwxr-xr-x 1 mysql dba   87208139 Jun  3 05:30 /data/install_mysql_5.6/mysql/bin/mysqld
-rwxr-xr-x 1 mysql mysql 87208139 Jun  3 05:30 /media/database/mysql/bin/mysqld
-rwxr-xr-x 1 root  root  87208139 Oct 13 11:51 /usr/bin/mysqld
-rwxr-xr-x 1 root  root  87208139 Oct 13 11:51 /usr/local/mysql/bin/mysqld
-rwxr-xr-x 1 mysql mysql 87208139 Jun  3 05:30 /var/lib/mysql/bin/mysqld

now:

find / -name mysqld | xargs ls -la
-rwxr-xr-x 1 mysql dba   87208139 Jun  3 05:30 /data/install_mysql_5.6/mysql/bin/mysqld
-rwxr-xr-x 1 mysql mysql 87208139 Jun  3 05:30 /media/database/mysql/bin/mysqld
-rwxr-xr-x 1 root  root  87987531 Oct 13 11:51 /usr/bin/mysqld
-rwxr-xr-x 1 root  root  87208139 Oct 13 11:51 /usr/local/mysql/bin/mysqld
-rwxr-xr-x 1 mysql mysql 87208139 Jun  3 05:30 /var/lib/mysql/bin/mysqld