Comment 10 for bug 1822738

I've looked as some /proc/meminfo dumps I was provided with.

Dump were made at these time points:
1. after boot
2. successful core refresh from 2.38 to 2.37.4
3. successful core refresh from 2.37.4 to 2.38
4. failed refresh of other snap, failed when mounting the snap with: fork/exec /usr/bin/unsquashfs: cannot allocate memory

This is a list of values that varied between dumps (with the exception of LowTotal and CmaTotal):
                     (1) (2) (3) (4)

MemFree: 4536 kB 11068 kB 23088 kB 52928 kB
MemAvailable: 163016 kB 163572 kB 163900 kB 155532 kB
Buffers: 29036 kB 30404 kB 15008 kB 1992 kB
Cached: 131148 kB 123692 kB 128144 kB 104288 kB
Active: 110720 kB 109724 kB 102740 kB 129208 kB
Inactive: 80724 kB 75892 kB 71808 kB 16128 kB
Active(anon): 33848 kB 34136 kB 33984 kB 41660 kB
Inactive(anon): 3160 kB 3160 kB 3160 kB 3160 kB
Active(file): 76872 kB 75588 kB 68756 kB 87548 kB
Inactive(file): 77564 kB 72732 kB 68648 kB 12968 kB
LowTotal: 243168 kB 243168 kB 243168 kB 243168 kB
LowFree: 4536 kB 11068 kB 23088 kB 52928 kB
AnonPages: 31304 kB 31568 kB 31416 kB 39092 kB
Mapped: 54896 kB 55140 kB 52052 kB 18556 kB
Slab: 23968 kB 23340 kB 22424 kB 21780 kB
SReclaimable: 11112 kB 11252 kB 10476 kB 9156 kB
SUnreclaim: 12856 kB 12088 kB 11948 kB 12624 kB
KernelStack: 1032 kB 1000 kB 992 kB 1008 kB
PageTables: 1064 kB 1044 kB 1044 kB 1060 kB
Committed_AS: 489144 kB 339420 kB 487848 kB 512848 kB
CmaTotal: 65536 kB 65536 kB 65536 kB 65536 kB
CmaFree: 2128 kB 208 kB 15752 kB 33700 kB

Interesting observations:
- MemAvailable stays high, consistent with top output recordings I was provided with previously
- CmaFree drops, that's the memory available to the contiguous memory allocation, IIRC that's for DMA transfers and such
- Slab unreclaimable (SUnreclaim) rises

Even though MemAvailable is high, launching new processes fails. CMA free falling is intersting, I would expect weird things to happen when it drops too low.

I think it would be worth collecting the output of:
- sudo cat /proc/slabinfo
- sudo slabtop -o

In the kernel source code, in tools/vm, there is a tool `slabinfo` which can process the data from /proc/slabinfo in a useful manner. If possible, I think it would be useful to rebuild the tool for given architecture and collect the output of:
- slabinfo
- slabinfo -T

Another angle that may be interesting to explore, just for the sake of making sure we check for the obvious things, is to collect this:
- cat /proc/sys/kernel/pid_max
- ps -efT | wc -l
- dmesg