Affinity Photo macOS: restricting memory seems to have no effect on performance

[nickbatz]

So I tried restricting the RAM use in Affinity Photo to 24GB. This was a poor man's test of whether I can get by with a Mac laptop that has a lot less RAM than the 64GB in my Mac Studio.

Surprise: the performance was at least as good as when I let it grab what it needs, and perhaps better - even when I loaded four very large pictures, each made up many pictures and well over 100 layers!

Does that make any sense?

[NotMyFault]

Do we really need another discussion about this topic? There are countless older discussions. Setting RAM limits in performance section is mostly irrelevant. it can preserve RAM for other apps running in parallel to Affinity apps, and improve their (other apps) performance. 

the OS will automatically compress RAM and use very fast SSD for memory paging so you won’t notice any performance reduction for Affinity apps.

Leave this setting alone, no need at all to fiddle with it.

[Pšenda]

7 hours ago, nickbatz said:

even when I loaded four very large pictures, each made up many pictures and well over 100 layers!

The information provided is definitely not sufficient to determine - how much memory is needed for their processing. I recommend launching Task Manager (or its equivalent in MacOs), and opening a project - which will actually use more than 24 GB of RAM, in your case ideally the mentioned 64 GB (perhaps by opening several projects at the same time). I would check how this project is being worked with - i.e. make some memory and computationally intensive adjustments, and only then would I try to reduce the limit for memory usage.

[Old Bruce]

16 hours ago, nickbatz said:

So I tried restricting the RAM use in Affinity Photo to 24GB. This was a poor man's test of whether I can get by with a Mac laptop that has a lot less RAM than the 64GB in my Mac Studio.

I think that you would need to have some applications open that are using 40GBs of RAM before you start Photo and then open a huge file.

[nickbatz]

12 hours ago, NotMyFault said:

Do we really need another discussion about this topic?

NotMyFault... the name sounds familiar. Were we classmates in charm school?

[nickbatz]

PEOPLE.

Please read the object of this exercise: I'm shopping for a new laptop and I wanted to do a casual check to see whether I can still work on my computer-taxing pictures in a cheaper laptop with less memory. The difference in price is significant.

I never expected this to be a scientific test, I was just surprised that Affinity Photo doesn't slow down when its RAM is restricted.

My regular machine is a Mac Studio with 64GB of RAM and memory is never an issue.

[HCl]

.

[R C-R]

4 hours ago, nickbatz said:

Please read the object of this exercise: I'm shopping for a new laptop and I wanted to do a casual check to see whether I can still work on my computer-taxing pictures in a cheaper laptop with less memory.

Hasn't your casual test told you what you want to know or are you looking for something more?

Edited November 15, 2024 by R C-R
Fixed typo "are" instead of "or"

[NotMyFault]

The memory setting has no positive effect in 99.9999% of all users and use cases. It is a relic from ancient times. You can worsen performance for Affinity apps without any gain for other apps. Ignore it. Leave it alone. Don’t touch it. Forget it. 
 

Period. Finish. Done. Finito. Basta. Fertig.

Modern OS including Windows, MacOS, iPadOS manage RAM for apps all the time. Never fiddle manually unless you are a kernel developer.

[nickbatz]

2 hours ago, R C-R said:

Hasn't your casual test told you what you want to know are are you looking for something more?

I'm certainly not looking for people to be nasty to me - and that doesn't apply to you

2 hours ago, NotMyFault said:

Modern OS including Windows, MacOS, iPadOS manage RAM for apps all the time. Never fiddle manually unless you are a kernel developer.

Oy gevalt! Yes, I know that - although if you use music software like I do, you often do have to consider memory use. But that's a different story.

Again: I'm not interested in the Affinity Photo memory setting. The only reason I did this was to see whether I could possibly use Affinity Photo the way I use it - which uses a lot of RAM - on a MacBook Air with limited memory.

My post was because I was surprised that it didn't slow down when allotted less RAM.

Basta finito etc.

 

[thomaso]

52 minutes ago, nickbatz said:

Yes, I know that - (…)

(…) The only reason I did this was to see whether I could possibly use Affinity Photo the way I use it - which uses a lot of RAM - on a MacBook Air with limited memory.

If you know how RAM gets managed by the OS … isn't it obvious that your test method can't deliver the wanted information?

If I understand right you run the test on your mac Studio with 64 GB RAM. – How about (if possible) removing some of the RAM hardware to experience a difference? However, the comparison may mislead if your Mac Studio uses Intel processors versus a mac with Apple Silicon/M.

[nickbatz]

28 minutes ago, thomaso said:

If you know how RAM gets managed by the OS … isn't it obvious that your test method can't deliver the wanted information?

If I understand right you run the test on your mac Studio with 64 GB RAM. – How about removing some of the RAM hardware to experience a difference? However, the comparison may mislead if your Mac Studio uses Intel processors versus a mac with Apple Silicon/M.

Actually it's not as obvious as it might seem. If you tell Affinity Photo that it can only grab, say, 16GB of RAM, one would expect that to simulate how it will behave if it only has 16GB of physical RAM available (leaving aside that the OS will use whatever it can use as well, and at this point I'm not considering a machine with less than 24GB).

I certainly don't expect this to answer my question beyond a doubt, it was just a first check. The real answer will be when I borrow a friend's machine.

Mac Studios use M chips, not Intel, and the memory isn't removable. That's one of the things that makes it hard to choose a machine these days: you can't change your mind later! But the jump from Intel to M chips was huge.

[NotMyFault]

5 hours ago, nickbatz said:

16GB of RAM, one would expect that to simulate how it will behave if it only has 16GB of physical RAM available

this expectation is wrong as the OS manages physical RAM and with help of CPU MMU provides virtual RAM to apps. Apps can only influence the amount of virtual RAM they request and use. The CPU / OS controls the mapping between both types. So limiting the virtual RAM use of one app is totally different from having less physical RAM.

On older Windows OS (until Windows 8/ 2008) you had the option to limit usage of physical RAM even for OS level (in a special section of  System configuration settings), and reboot the PC. We had one user who used one specific very old app which did not run if too much RAM was available. Originally, the user opened his PC and removed RAM, rebooted the PC when he run this ap. Afterwards he installed RAM again to run other apps. When we learned about this we showed him the trick to do this by an OS setting and he was very happy as it saved him from the daily procedure.

Im not aware that such settings exists on MacOS, it is possible.

On M1 based (and later) things become more complex based on the shared RAM between CPU and GPU.

The only way to check if one or multiple apps run on a system with less RAM is to test on such a machine, or limit physical RAM usage of the OS (not of any app).

The type and size of display may play a role, too.

 

PS: on server with capable OS (including Windows data center) you can actually add or remove RAM while fully running! The MMU inside the CPU rearranges the mapping of vRAM to pRAM for all running apps, and/or intensifies paging to disk. 

[James Ritson]

Some background: RAM usage limit affects the size of the bitmap cache held in volatile memory. Data that exceeds the bitmap cache size will be written off (paged) to a backstore file on the OS disk, then retrieved again when necessary. Users of Publisher will tend to see this behaviour the most when working with lots of high resolution imagery throughout multiple page documents: images may appear low resolution/blurry for a time until they "resolve" to their more detailed copies. The efficiency of this process will be determined by the current memory status, e.g. how saturated the current memory usage is, whether other data held in memory has to be written off to the backstore file before the requested data is loaded in etc.

It doesn't constrain how much total memory the apps are allowed to allocate, so you can't use it to emulate the behaviour of a machine with less RAM installed. Reducing the usage limit arbitrarily would also modify the status thresholds for memory management, which could influence when to degrade user experience to salvage memory—this might include slow generation of mipmaps (or in extreme cases, not at all), dumping large bitmap caches that can always be rebuilt later and so on.

The architecture of modern Apple Silicon devices lends itself well to more "aggressive" memory management (which macOS has employed for quite a while now), and we tend to see lots of exaggerated claims of "you only need 8GB", "8GB on Apple Silicon is like 16GB on x86!" etc. Whilst the Affinity apps are certainly serviceable on 8GB, you can't really get around physical limitations—e.g. requirements of uncompressed bitmaps that must be held in memory—so you should always go for as much RAM as you can afford that makes sense for your workflow. If you're just casually editing basic images, 8/16GB is likely fine. If you're placing hundreds of images into a publication and manipulating them with adjustments, or working on multi-layer compositions in 16-bit or 32-bit per channel precision, you'll get a smoother experience with more memory headroom.

Hope the above is helpful!

[nickbatz]

9 hours ago, James Ritson said:

 

Hope the above is helpful!

Very. Thanks.