Hello everyone, I've been trying to understand the role of the pagecache, starting with drop_caches and observing what it does. From my understanding of the code (fs/drop_caches.c) , it walks over all the open files/inodes, and invalidates all the mapped pages. Pages which are *not* dropped are either dirty,in-use,anonymous,mapped(to pagetable),or writeback) . Is my understanding correct? But, when i run drop_caches, there are still some pages which show up as cached. Why arent all cache pages getting dropped ? My confusion runs much deeper. What exactly constitutes the pagecache? All filebacked pages ? mmaped files ? If i copy a bunch of files, why does my cache get polluted with those pages? Thanks for reading. I'd be grateful if someone can enlighten me about some pagecache internals . (Please keep me CC'ed) <begin experiment> root@tripitz:/etc/apt# free -m total used free shared buffers cached Mem: 1995 1854 140 0 79 700 -/+ buffers/cache: 1074 920 Swap: 4767 762 4005 root@tripitz:/etc/apt# echo 3 > /proc/sys/vm/drop_caches root@tripitz:/etc/apt# free -m total used free shared buffers cached Mem: 1995 1373 621 0 0 363 -/+ buffers/cache: 1009 985 Swap: 4767 762 4005 <end experiment>