Mapped more than Cached in /proc/meminfo

[=/_00/\/\]

Hi,

Please find my reply inlined.


On Wed, Aug 10, 2011 at 1:04 PM, Prateek Sharma <prateek3.14 at gmail.com>wrote:

>
>
> On Wed, Aug 10, 2011 at 12:56 PM, Mulyadi Santosa <
> mulyadi.santosa at gmail.com> wrote:
>
>> Hi///
>>
>> On 09/08/2011, =/_00/\/\ <z0032oom at 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.)
>

But even in this case Cached (/proc/meminfo) should be always greater than
Mapped(/proc/meminfo)  (As it will contain mapped  + Unmapped pages)
I also saw that Cached (/proc/meminfo) does not include Buffer Cache.

========= fs/proc/meminfo.c ========
cached = global_page_state(NR_FILE_PAGES) -
                        total_swapcache_pages - i.bufferram;
==============================

Even if drop_cache is not done is it ever possible to get Cached < Mapped ?



Regards,
  ~/
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