com.apple.photomodel uses 38GB real memory or 198GB virtual memory even after Photos closed on High Sierra

Use Activity Monitor to force quit the memory hogging process. Something went wrong with that. It should restart automatically and not use such an inordinate amount of memory.

Using programs like memory clean does not solve problems like this and can prevent your system from working as designed. Since Mavericks the OS handles memory allocation and reuse in such a way that programs like this one (which try to force the purging of “inactive” memory) actually DECREASE system performance. There was a time when such programs were marginally useful. Now they should NOT be used.

Ivan H wrote:

...Besides, Memory Clean (now, Memory Clean 2) helps a lot in releasing memory on MBA. Your comment "Using junk..." is your personal opinion. In my experience with Memory Clean, I have never come across anything from it "preventing" my Mac from working properly. So, you're welcome to substantiate with evidence about "prevents your Mac from working properly".

If you need to substantiate with evidence then uninstall the App and see what OS X is telling you without the junk-ware interfering with the OS. If you need more evidence you can search the forums here and see where junk like Memory Clean and dozens of other products; many of which are sold on the App Store are the first offenders with system destabilization and when they are removed problems go away.

For futher analysis you may post an Etrecheck report. The link is http://www.etrecheck.com

Do as you please, but using totally worthless garbage products like "memory clean" will only exacerbate whatever the problem may be, if there is one, which is questionable. macOS manages its memory resources to obtain maximum performance. Interfering with it can only degrade performance and accelerate hardware failure.

Rule 1 of Macs is don't install junk. Those things don't fix problems. They cause them. Good luck!

I don't know why photomodel would be using such much memory. It is indeed excessive.

BUT... note that most of it is compressed.

That IS the memory management of macOS doing its work.

Otherwise you would need more than 200GB of swap space.

Stuff like memoryclean have no notion of compressed memory.

Compressed memory is much faster to retrieve than if it had been swapped to disk instead.

CPU (needed to compress and decompress) and RAM are orders of magnitude faster than the SSD (and HD is yet an order of magnitude slower than SSD, as we all know).

Ivan H wrote:

A lot of uni students use those "junk" products because their MacBook Airs have 4GB/8GB and while doing research requires a lot of documents stay open. The garbage collection (of memory) of OS X is famously bad! That gives the Memory Clean or similar products a niche to survive. Memory Clean worked very well in the past. It's upgraded version of Memory Clean 2? Not bad, from empirical experience.

The predictable abundance of ignorant, gullible consumers gives the Memory Clean or similar products a niche to survive. It's a multi-billion dollar industry, and you are its ideal customer.

Ivan H wrote:

Btw, I think compressed memory used 28GB of physical memory, 244GB compressed memory were swapped to the slow Fusion Drive.

No, 244GB compressed memory means that a portion of memory worth 244GB, and which not being actively used by the application, is compressed to save space.

The compressed version is stored in memory whenever possible.

For example, looking at Activity Monitor right now the total of my Compressed Memory column is a few GB, and Swap Used is only 200MB.

The idea is that compressing and decompressing is much faster than swapping.

In the illustration of my screenshot above, the swap used was 49.91GB! Memory used by the com.apple.photomodel was 38GB and left no space for other apps / processes to run.

No dispute to the fact that 49.91GB of swap is huge, and 288GB of RAM is huge, and should NOT normally happen.

Now that a few days have passed, I imagine you have force-quit the wayward process, so the question is: does it recur? Or was it a one-off thing that went haywire?

Using junk like “Memory Clean” prevents your Mac from working properly.