[maleadt]

Outside the LTS stack, pooled memory is now released with ZE_DRIVER_MEMORY_FREE_POLICY_EXT_FLAG_DEFER_FREE instead of a blocking free. Because kernels access memory indirectly, a blocking free waits for all work submitted so far. From a finalizer, that stalled the thread (~860 ms behind a busy kernel in the measurements on #717), and it deadlocked when that work waited on a task on the same thread.

NEO only processes its deferred-free list during a later free (or when an allocation fails), so memory released this way could stay allocated indefinitely. sweep_deferred_frees frees a small dummy host allocation with the deferring policy, which processes the list without waiting for the GPU. It runs where we try to get memory back: after each GC in retry_reclaim, after trimming the pools in _maybe_gc, and after the scratch hedge's GC.

The LTS stack keeps the old behavior (synchronize, then a blocking free). NEO doesn't report which free policies it supports, so this relies on the rolling stack implementing DEFER_FREE.

Tests:

• freeing a large array while a kernel waits on the host no longer blocks (it hangs on main);
• a deferred free is not processed while the GPU still uses the memory, and is processed by a sweep once the GPU is done.

Part of #717. Not covered yet: the finalizer of a busy immediate command list still drains it, and the LTS path still blocks.

[codecov]

Codecov Report

❌ Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.49%. Comparing base (e95e38f) to head (f6be2c5).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pool.jl	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #720      +/-   ##
==========================================
- Coverage   84.08%   82.49%   -1.59%     
==========================================
  Files          52       51       -1     
  Lines        4386     4268     -118     
==========================================
- Hits         3688     3521     -167     
- Misses        698      747      +49     

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