On Wed, Aug 10, 2011 at 12:56 PM, Mulyadi Santosa <mulyadi.santosa@gmail.com
wrote:
Hi///
On 09/08/2011, =/_00/\/\ <z0032oom@gmail.com> wrote:
Hi,
Thanks for replying Here is one observation worth mentioning. On boot system it shows Mapped < Cached (In fact much less)
quite predictable.... during booting phase, your system read() much by doesn't mmap() that much....
After using system for some time following commands are executed. # sync and echo 3 > /proc/sys/vm/drop_cache
Whenever above command is executed I can see Mapped > Cached.
by echoing "3" to drop_cache, you flush the content of page cache as much as possible ...
Here is my understanding of what drop_page_cache does: All page-cache pages are 'dropped' except the following: 1. Dirty pages. (they are *not* synced) 2. Mapped pages (pages 'in use' , mapped by rmap ) (There are a few more exceptions i dont recall now.) Hence even after dropping caches, free will still show some cached pages. These are dirty+mapped. Doing a sync before dropping will only show the mapped pages.