mem.info()s max free sz meaning?

[kjm1102]

I'm getting memory allocation errors when I try to put ~20kb files into ram. So I'm trying to decipher mem.info() to figure out where the problem is.

>>> mp.mem_info(1)
stack: 492 out of 7936
GC: total: 192064, used: 5008, free: 187056
 No. of 1-blocks: 59, 2-blocks: 15, max blk sz: 64, max free sz: 11675
GC memory layout; from 2000c680:
00000: h=MhhBDhhBTTBDBDBhTh===BBh=Dh====B=BBBBBBTB=BTB=BBBTB=TBTB=Bh===
00400: DB=h===========h===================BBBh==h=h=====h==============
00800: ===h============================================================
00c00: ===h============================================================
01000: ===h=BhhhBSh====h=h=hThh=BShhh====Thhhh=B...........h=.....h====
01400: ===h=====.......................................................
       (181 lines all free)
2ec00: ....................................

This says 187056k free in 181 lines (the dots) that look contiguous each line presumably 187056/181=~1k, Next I try to reserve 20k of ram

>>> a=bytearray(20000)
>>> mp.mem_info(1)
stack: 492 out of 7936
GC: total: 192064, used: 25200, free: 166864
 No. of 1-blocks: 65, 2-blocks: 18, max blk sz: 1250, max free sz: 10416
GC memory layout; from 2000c680:
00000: h=MhhBDhhBTTBDBDBhTh===BBh=Dh====B=BBBBBBTB=BTB=BBBTB=TBTB=Bh===
00400: DB=h===========h===================BBBh==h=h=====h==============
00800: ===h============================================================
00c00: ===h============================================================
01000: ===h=BhhhBSh====h=h=hThh=BShhh====Thhhh=Bh=BAhhB..h.h=.....h====
01400: ===h=====h=h====================================================
01800: ================================================================
01c00: ================================================================
02000: ================================================================
02400: ================================================================
02800: ================================================================
02c00: ================================================================
03000: ================================================================
03400: ================================================================
03800: ================================================================
03c00: ================================================================
04000: ================================================================
04400: ================================================================
04800: ================================================================
04c00: ================================================================
05000: ================================================================
05400: ================================================================
05800: ================================================================
05c00: ================================================================
06000: =============================================.....h=............
       (162 lines all free)
2ec00: ....................................

Yep, that makes sense, 20k less memory than before. But I can't figure out what max free sz means? It's hardly changed? To me the max free sz should be the largest number of contiguous lines multiplied by the ~1k bytes/line? Can someone enlighten me?

[jimmo]

It's the number of blocks in the largest contiguous run of free blocks.

See more details here https://github.com/orgs/micropython/discussions/11997

[kjm1102]

So when I reduced free ram from what looks like 181 contiguous lines to 162-5=157 contiguous lines with the 20k byte array why does the max free blocks hardly change? Is it because the max blk size has increased from 64 to 1250? If so why does allocating some ram to a bytearray cause a change in max blk size?

[jimmo]

>>> 11675-10416
1259
>>> _*16
20144

So the max free size decreased by 1259 blocks, corresponding to the 20kiB you allocated.

[kjm1102]

So a block is always 16 bytes? If so why is there a max block size & why does it change from 64 to 1250?

[jimmo]

A block is always 4 words, so 16 bytes on 32 bit systems.

The max size is the size of the largest allocation (in blocks).