Questions about Defragmentation Thread Safety

[rbertin-aso]

Hello Adam !
Small question regarding defragmentation.

In the documentation it is written :

What it means in practice is that you shouldn't free any allocations from the defragmented pool since the moment a call to BeginPass begins.

One solution that you give is :

A solution to freeing allocations during defragmentation is to find such allocation on the list pass.pMoves[i] and set its operation to D3D12MA::DEFRAGMENTATION_MOVE_OPERATION_DESTROY instead of calling allocation->Release()

However, it is only possible to set the operation after having the pass moves (after the return of the call). Do I need to keep track of allocations that want to be released during computation time or won't it be an issue if releasing occurs ? Could it be simpler to just add a reference to allocations that ends up being part of a move and remove a reference at the end of the pass ?

Hope those questions are not stupid :)
Have a nice day !

[adam-sawicki-a]

You are right. Just as the documentation says, allocations that can be defragmented shouldn't be released since the moment a call to BeginPass starts. I recommend to store the list of allocations to be released and defer this release to the time after the defragmentation pass is complete.

I think calling AddRef and Release to manage reference counter of all the defragmented allocations would add too much of unnecessary performance overhead.

[rbertin-aso]

Thanks for those answer. I will then prefer the list of allocations.

[rbertin-aso]

Hello again Adam. Sorry for reopening this ticket. After reading again the documentation to be sure, I noticed this sentence :

Otherwise, a thread performing the allocation->Release() would block for the time BeginPass executes and then free the allocation when it finishes, while the allocation could have ended up on the list of allocations to move.

Is it okay to keep every allocation that need to be release into a list (that will be released after the EndPass) between the beginning and the end of BeginPass and after the end of BeginPass to keep in the list only allocations that are into the pass movements ?
To rephrase, is releasing allocations that aren't pass movements an issue if BeginPass is done ?
(I'm trying to optimize the number of allocations that go into that list because between Begin and End, it can be a lot ! )

Have a nice day !

[adam-sawicki-a]

You are right, this optimization is correct. After BeginPass call finishes, only allocations that ended up on the list of movements should not be released. Other allocations can be released and new allocations can be made between BeginPass and EndPass.

[rbertin-aso]

Okay thanks a lot !

new allocations can be made

I'm afraid of this :). Do you mean allocations must not be made during BeginPass or just that they will be blocked by the mutex ?

[adam-sawicki-a]

They will just be blocked by the mutex and then execute after BeginPass, which is fine.

[rbertin-aso]

Okay ! Thanks a lot for those answers !
I'm closing until next questions :D