Previously ReleaseBuffer did not immediately null out the buffer, instead the releaseBufferOnCommit flag allows it to be nulled when the texture is next access and the pending changes from the buffer are committed to it. Now the texture is committed immediately, thus the buffer is null once ReleaseBuffer returns.
Once loaded, we force a GC to reclaim temporary memory used during loading. Previously the buffer would not be null as it was pending commit to the texture and thus could not be reclaimed. As soon as we rendered the first frame, the buffer is nulled but we are now in a low GC state - and the buffer will not be reclaimed until the next gen 2 GC which may be dozens of minutes away.
This change ensures the buffer is null in time for the post-load GC, and thus can be reclaimed before we start rendering.
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