memory usage between kernel versions

[Mike Harless]

Hi,

I've got an embedded product that is currently using a 3.14 kernel, with
all user apps compiled with gcc 4.9 against that kernel.  When I replace
the 3.14 kernel with a 4.9 kernel, and leave everything else the same on the
product, I see my memory available drop by over 10MB when looking at
/proc/meminfo.  The size difference between the 3.14 and 4.9 kernels is
only about 1MB, so I'm trying to figure out where the rest went, and if
I've possibly configured somehting in the 4.9 kernel differently that's
causing the change.

Looking at smaps files for various processes, I'm seeing some Rss
differences when some common libraries are loaded and I'm wondering if
it's really different, or just different accounting/fetching.  For
instance, with libc and the same process with both kernels:

3.14 kernel:
4c010000-4c0d0000 r-xp 00000000 00:0e 1177 /lib/libc-2.20-2014.11.so
Size:                768 kB
Rss:                 416 kB
Pss:                  12 kB

4.9 kernel:
4c010000-4c0d0000 r-xp 00000000 00:0e 1177 /lib/libc-2.20-2014.11.so
Size:                768 kB
Rss:                 768 kB
Pss:                  12 kB

Is this difference in Rss something to keep looking into, or are there
other thoughts or suggestions on where to look?  Thanks!


--Mike