I'm thinking yet another way to purge. It might not need to use idle tasks, but low priority tasks and it would purge only to the default levels, not purge all. That might make this less risky from memory usage point of view. Investigating... but feel free to review the patches anyhow. That extra purging would be a followup patch or bug.
Bug 1815069 Comment 5 Edit History
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I'm thinking yet another way to purge. It might not need to use idle tasks, but low priority tasks and it would perhaps purge only to the default levels, not purge all. That might make this less risky from memory usage point of view. Investigating... but feel free to review the patches anyhow. That extra purging would be a followup patch or bug and would be needed only if memory usage turned out to be too high.