Thank you Ankit! I've attached the blend file I'm using.

From the Texture Paint screen, after creating a new image, I select Mode - Single Image, attach my Image file, and then when I attempt to paint the image, it freezes, then the memory spike happens, please see the image I've attached, where I've circled the step I take before it crashes.

In the Youtube link in my first post, it happens after the 2:35 time mark, where the Youtuber is able to paint their model, mine will crash.

I had to force quit, when it exceeded 4 GB quickly. Got this in trace:

#0	 in do_projectpaint_thread at blender/source/blender/editors/sculpt_paint/paint_image_proj.c:5336
#1	 in BLI_task_pool_work_and_wait at blender/source/blender/blenlib/intern/task.c:937
#2	 in project_paint_op at blender/source/blender/editors/sculpt_paint/paint_image_proj.c:5665
#3	 in paint_proj_stroke_ps at blender/source/blender/editors/sculpt_paint/paint_image_proj.c:5765
#4	 in paint_proj_stroke at blender/source/blender/editors/sculpt_paint/paint_image_proj.c:5806
#5	 in paint_stroke_done at blender/source/blender/editors/sculpt_paint/paint_image.c:632
#6	 in stroke_done at blender/source/blender/editors/sculpt_paint/paint_stroke.c:994
#7	 in paint_stroke_modal at blender/source/blender/editors/sculpt_paint/paint_stroke.c:1448
#8	 in wm_handler_operator_call at blender/source/blender/windowmanager/intern/wm_event_system.c:2006
#9	 in wm_handlers_do_intern at blender/source/blender/windowmanager/intern/wm_event_system.c:2787
#10	 in wm_handlers_do at blender/source/blender/windowmanager/intern/wm_event_system.c:2835
#11	 in wm_event_do_handlers at blender/source/blender/windowmanager/intern/wm_event_system.c:3230
#12	 in WM_main at blender/source/blender/windowmanager/intern/wm.c:447
#13	 in main at blender/source/creator/creator.c:524

The code works as designed. But it is a problem to have no safeguard or warning to avoid things like that.
The UV of your object is very high and any operation is working on the entire texture at once and several times.
Edit the UV of your object before working on the texture.

Although it's not really broken, I don't think such a problem should be ignored. At least it must be a task for T68896: Texture painting usability

@Germano Cavalcante (mano-wii): I think this should be a Known Issue then?
(feel free to change back though -- but usually out-of-memory issues are not considered bugs)

Most of the time, it skyrockets to 20GB+ for no reason at all. I guess its a huge memory leak.

Just to make this clear: we are having UVs with values like 3000 [instead of 0-1 or at least something more sensible...]
Just quickly packing UVs here make will get rid of the memory spike:

I havent checked code here, and of course it would be good to reduce the cost even with huge UV maps, but still think there is no reason to have UVs with these astronomic values as well...

@Ankit Meel (ankitm) : not sure T75452 has the same roots... In T75452, the UVs all seem to ly inside a 0-1 range...

oh sorry, Please reopen