On Wed, Aug 10, 2011 at 12:56 PM, Mulyadi Santosa
<mulyadi.santosa@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.