I tried to increase the PHP Memory limit but it didn’t work, so I looked into the web how to increase APC (cache) memory.
I share it in case it may be useful to someone else.
Edit the file
/etc/php.d/apc.ini and set
apc.enabled = 1
apc.shm_segments = 1
apc.shm_size = 256M
apc.ttl = 7200
apc.user_ttl = 7200
apc.gc_ttl = 0
apc.mmap_file_mask = "/tmp/apc.XXXXXX"
Restart web server Apache.
For display exact APC memory usage i have copied
/usr/share/phpldapadmin/htdocs/apc.php and load
source for apc settings and display APC cache information: