fseventsd shows high memory usage on Mac Studio M5 overnight

Native Synch and Backup programs like iCloud Drive and Time Machine that DO use the MacOS File System Event Store can find changes really quickly and be done with their work and suspend themselves. Time machine can run backups Hourly, while all those others are still beating on the file system for the first pass, four hours later. By the time those others have finished one pass, they need to start again.

This large use of RAM is very likely to be caused by your Non-native File Sync-ers:  Dropbox, BackBlaze, OneDrive, Carbonate, or Google drive and others are in this category. Since they were ported from that other OS environment, they IGNORE the Mac File System Event Store (that could tell them EXACTLY what folders have changed recently). 

Instead, they do a a Brute-force read of all your files, and all the files stored on their drive on the Internet. This punishes the ability to get any data (including speed test data) through their enormous and frivolous file reading and re-reading.

They are also 'on the phone' checking and re-checking the synced file stored on the internet. Between constant scanning and constant Internet access, this uses a LOT of resources -- far more than Apple-native File-Syncers like iCloud. Running File-Syncers when not actually needed still consumes a lot of computer resources. 

Also, because your Mac tries to cache these reads for rapid-re-use, the amount of free RAM consumed for these references goes up. it can be freed when you need large amounts of free RAM, but will pnly be freed automatically on a least-recently used basis.

Unused memory is wasted memory. macOS is designed to utilize hardware resources to their greatest extent. If that Mac had 128 GB "Backblaze" would probably consume even more.

The difference between it and the limit of installed memory is likely to be whatever else the Mac is doing at the time.

Could this be related to initial file indexing/background processing ...

Both. Among other tasks fseventsd keeps track of file changes throughout the system so it would be expected to be consuming resources when backup software is in use.

It's normal and there is no reason for concern.

1) The fseventsd process is a File System Events Daemon. Basically it's a background system service, that tracks changes to files and folders on your backup drives and external volumes.

2) Sleep mode is not as straight forward as it used to be. There are different levels of sleep and all sorts of Funky things can happen depending on Energy settings, connected devices and third-party software.

While it sounds like Backblaze maybe or have been the worst offender, issues can crop up from other types backups and Energy settings.

With that in mind, open your Energy settings and post a screenshot of your current Energy panel settings.

As you demonstrated yourself by your numbers dropping precipitously after disabling BackBlaze,

you do not have a large memory consumption issue of any kind.

What is "Not Normal" is doing backups onto the Internet.

"On the cloud" is great for sharing photos, but is not a viable backup solution for everything you have. The stuff is not under your control, and is subject to sloppy handling, arbitrary changes in policy, theft, accidental deletion, data loss [are they making frequent backups using best practices?], and discontinuation or throttling of the service. It can easily take three days to restore it at ordinary Internet speeds.

Summary:

No, I do not think you have a memory leak or any system defect except:

'choosing to use third-party "ported" software and storage on the Internet to hold you backups.'

^--- THAT is nonsense.

Keøps wrote:

• During the day, memory usage remains stable, even when actively using the Mac.

• The Mac itself remains responsive, with normal memory pressure and no crashes or slowdowns.

• Restarting resets fseventsd to approximately 5 MB.

So, this is a transient effect, overnight, when the Mac is not otherwise in use. Daytime, in use, there seem to be no issues.

Backblaze was performing its initial backup of approximately 600,000 files. I noticed high CPU and memory activity from both Backblaze and fseventsd at the same time.

For what reason would you consider that abnormal during a backup run of 600K files? I think it's to be expected.

Are you saying fseventsd doesn't release the memory and that you have to restart to kick it back down?

However, what really concerns me is that the fseventsd process reached 79 GB of RAM, ...

What does "reached" mean?

If you are asking about the cumulative amount of memory used by any particular process, it's a meaningless value. The only parameter that matters is Activity Monitor's unitless Memory Pressure graph, since it can be used to visually confirm a Mac's performance is being constrained by a lack of memory. That would become evident in quantifiable performance degradation before anyone would have reason to investigate potential causes through Activity Monitor.

Even it does not matter since there is nothing you can do about it, other than to uninstall or not use the software you chose to install. Presumably you had reason for deciding upon "Backblaze" for whatever benefit it may convey for your particular needs, and like any other software it is going to exploit whatever resources macOS permits it to use.

If you don't like a particular product's effect on your Mac's performance, you don't have to use it, but unless I'm missing something your Mac's performance does not appear to have been affected by "Backblaze".

I’m particularly concerned about having to reinstall macOS or start configuring everything from scratch again.

There is absolutely no justification for that.

By all means if I'm overlooking some kind of problem with that Mac explain what it is.