So I tried to enable filecache with following settings:
$wgUseFileCache = true;
$wgUseGzip = true;
$wgFileCacheDirectory = "/var/cache/mw-filecache";
mw-filecache folder were set to 777, php-zlib installed. But nothing generated. So I tried RebuildFileCache.php. Then all the pages showing:
Page 'xxx' (id 962) not cacheable
How can I identify the cause of this "not cacheable" problem?