Ignore already generated chunks, to reduce resources used? (1.10.2/1.5) about chunkgen HOT 4 OPEN

That's odd, because I just ran a 400 radius gen last night on a server with 3GB allocated and it went just fine, memory use stayed constant the whole time.

And I'm pretty sure the way the logic works is it calls for chunks to be loaded, and if they don't exist the server creates them. But if they do exist, loading is pretty much instant, and then they get unloaded. I definitely noticed that when I first started the chunkgen task, it blew through the first bunch of chunks really quickly because they already existed, then slowed down a bit when it had to start generating new ones.

Anyway, finished chunks should definitely be getting unloaded as it goes, so memory usage shouldn't keep going up.

What modpack are you using?
And JVM args are an arcane art that most people don't know what any of them mean, and depend on the circumstances. For example, the CMS garbage collector has traditionally been recommended for Minecraft servers, but in the case of hardcore chunk generation overnight where no players are on and you're not worried about TPS, sometimes the serial throughput collector could be faster.

These days though, if you're running Java 8 and Minecraft 1.10, I'd suggest switching to the G1 GC.
I'm not going to write a full guide on profiling memory usage and setting correct GC parameters here, but I did base my research on Aikar's work (https://www.spigotmc.org/threads/guide-optimizing-spigot-remove-lag-fix-tps-improve-performance.21726/page-10#post-1055873)

Yes, I had VisualVM open and was watching memory activity while Chunkgen was running, so here's some guidelines from what I've found. The static (Old Gen) usage may vary by modpack, but most med-size packs these days will be roughly the same. I'm using FTB Infinity Lite 1.6.0 on MC 1.10.2, Java 8_102, FreeBSD, 4GB RAM server, 3GB given to Java.

-XX:MetaspaceSize=200M
-XX:MaxMetaspaceSize=300M
-XX:+UseG1GC
-XX:+UnlockExperimentalVMOptions
-XX:MaxGCPauseMillis=50
-XX:TargetSurvivorRatio=90
-XX:G1NewSizePercent=40
-XX:G1MaxNewSizePercent=75
-XX:InitiatingHeapOccupancyPercent=15
-XX:G1MixedGCLiveThresholdPercent=50

Again, Aikar's post walks through what most of those actually do, my point was I've tested that they actually behave correctly for this specific situation. Old Gen stays nearly constant at 1.15GB used / 1.74GB allocated, Eden (New) space allocates roughly 1.2GB, and fills at around 60MB/s, with cleanups of 50ms every 15s or so:

The point is you want to make sure that all those chunks being generated, loaded and unloaded stay in the Eden space so they can be cleaned up quickly, not filling up the Old gen where it takes much longer to empty and leads to Out of Memory situations.

If you've got more than 4GB of memory to allocate to Minecraft (And if it's a desktop computer, not a dedicated server, don't throw more than half of your system's total RAM at it), try setting -XX:G1NewSizePercent=50, which will leave plenty of room in Old Gen for even a rather large modpack to live, and lots of Eden space for the chunks to get loaded in, and unloaded before they get moved to Old.

And that was far more than I planned on writing, but I have dealt a lot with optimizing Java's GC for running large modpacks on small servers, and handling worldgen without lagging as much. (Mods that add things to worldgen are a completely different issue, you can still get lag with players online and exploring new chunks, as then you're CPU-bound, not out of memory. But that's why we're pre-generating the world)

TL;DR:
Chunkgen is doing its job properly, most JVM settings are irrelevant, but try using the G1 GC, tuned to give lots of space to NewGen.

from chunkgen.

I was probably using really old launch commands. Plus, I'm going through SkyFactory 3 right now, which doesn't require stupid amounts of RAM. When/if I restore my old world, I'll definitely use the new commands (I'm also going to restart my server using these new commands).

However, my original question was if logic existed to skip already generated chunks, as opposed to going through them (not regenerating of course) from 0.

from chunkgen.

I don't know if there's a way to automatically know what chunks exist or not, but there is actually a config option to skip X chunks at the start. You just have to figure out how many need skipping yourself.

There's also a config option for max chunks to have loaded that you might want to play with.

Go check out chunkgen.cfg.

# Configuration file

general {
    # Height starting value
    I:height=0

    # Pause chunk generation if more chunks than this are in memory
    I:maxChunksLoaded=3000

    # Number of chunks loaded per tick
    D:numChunksPerTick=1.0

    # Pause chunk generation when players are logged on
    B:pauseForPlayers=false

    # Skip a number of chunks at start of generation. Set automatically.
    I:skipChunks=1255317

    # Number of chunks inbetween percentage updates
    I:updateDelay=40

    # Width starting value
    I:width=0

    # X starting value
    I:x=0

    # Z starting value
    I:z=0
}

from chunkgen.

I am also not able to generate the desired map for my server. I usually do it every night to avoid causing lag to my users, but it is too slow and I always load the already generated chunks, taking longer than expected, even in the whole night barely gets to generate 0.5%
I have already uploaded the memory and the amount of chunks per tick but nothing makes it go faster.

from chunkgen.