Why UnregisterMemory in PreFreeMemory instead of PerformFreeMemory ?

[Jianxiao Lu]

In MemoryAllocator, there is a member variable size_ to record current committed memory size..
The size_ increase after allocate or commit a VirtualMemory.
From the perspective of symmetry, the size_ should decrease after free or uncommit a VirtualMemory .
But in fact it's in PreFreeMemory.
When free pages with mode kPooledAndQueue, the size_ will decrease during UnregisterMemory during PreFreeMemory, but the MemoryChunk is not really freed or uncommitted.

I think the decrease of size_ should be in PerformFreeMemory.
I wonder what is the purpose of the current design?

[dinf...@chromium.org]

Hi,

this is indeed surprising. I suppose the main reason for this behavior is that we record memory size before and after the GC (see https://source.chromium.org/chromium/chromium/src/+/main:v8/src/heap/gc-tracer.cc;l=330). If we would decrement size_ some time after that point, we wouldn't see that memory size decreases after a GC.

Regards,

Dominik

[Jianxiao Lu]

Thanks for the explanation, it make sense to me, and I find that the MemoryAllocator is refactored, it's readability is better now.

Regards,

Jianxiao