embedded Linux RAM usage and confusion - memory

Question

I am trying to optimize RAM for an embedded Linux.
Running in same hardware, pretty much same software one is old version (yocto morty) and another is new version (Yocto dunfell).
free for new version
total used free shared buff/cache available
Mem: 57568 41020 2036 324 14512 12520
Swap: 0 0 0
free for old version
total used free shared buff/cache available
Mem: 57496 34120 2588 284 20788 19516
Swap: 0 0 0
I can see used memory increase about 7M for new version.
when I do ps axo pid,rss,cmd | awk '{sum+=$2} END {print sum }'
and sum up all the RSS value for my system.
I found my new version(83652K) actual less than old version(124240K). Nearly every process RSS is smaller than old version.
It does not make sense to me.
So I use the cat /proc/meminfo to get more detail.
I found the key different is Active(anon) and AnonPages. New version increases 6M.
But I don't know where this 6M comes from and how to trace it.
Thanks
*****************new version***********************
MemTotal: 57568 kB
MemFree: 1460 kB
MemAvailable: 14752 kB
Buffers: 132 kB
Cached: 11760 kB
SwapCached: 0 kB
Active: 31456 kB
Inactive: 4044 kB
Active(anon): 23720 kB
Inactive(anon): 212 kB
Active(file): 7736 kB
Inactive(file): 3832 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 12 kB
Writeback: 0 kB
AnonPages: 23628 kB
Mapped: 6712 kB
Shmem: 324 kB
Slab: 10464 kB
SReclaimable: 5300 kB
SUnreclaim: 5164 kB
KernelStack: 1496 kB
PageTables: 1948 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 28784 kB
Committed_AS: 651316 kB
VmallocTotal: 958464 kB
VmallocUsed: 1228 kB
VmallocChunk: 951436 kB
***********old version**************************************************
MemTotal: 57496 kB
MemFree: 1996 kB
MemAvailable: 19172 kB
Buffers: 908 kB
Cached: 12092 kB
SwapCached: 0 kB
Active: 30168 kB
Inactive: 812 kB
Active(anon): 18048 kB
Inactive(anon): 216 kB
Active(file): 12120 kB
Inactive(file): 596 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 52 kB
Writeback: 0 kB
AnonPages: 17984 kB
Mapped: 5984 kB
Shmem: 284 kB
Slab: 14188 kB
SReclaimable: 8036 kB
SUnreclaim: 6152 kB
KernelStack: 1480 kB
PageTables: 2120 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 28748 kB
Committed_AS: 649728 kB
VmallocTotal: 958464 kB
VmallocUsed: 1228 kB
VmallocChunk: 951556 kB