LuciferYang commented on code in PR #12443:
URL: https://github.com/apache/gluten/pull/12443#discussion_r3520249028
##########
gluten-core/src/main/java/org/apache/gluten/memory/memtarget/OverAcquire.java:
##########
@@ -18,29 +18,34 @@
import com.google.common.base.Preconditions;
+/**
+ * Wraps {@code target} and, on each successful {@code borrow}, performs a
preemptive spill probe
+ * against {@code overTarget}.
+ *
+ * <p>The probe asks {@code overTarget} to borrow {@code ratio *
target.usedBytes()} bytes, then
+ * immediately releases them. Because {@code overTarget} shares Spark's memory
pool with {@code
+ * target}, the borrow call forces Spark to spill other memory consumers if
the pool is tight, and
+ * the subsequent repay frees the reservation without holding any actual
memory. The net effect is
+ * that subsequent allocations under {@code target} start with the pool in a
shrunk state and are
+ * less likely to hit an OOM that {@code target} itself cannot spill out of
(for example, a two-step
+ * reservation where step A is spillable but step B is not).
+ *
+ * <p>Historically the over-acquired memory was held for the lifetime of the
reservation as a backup
+ * for OOM; that shape was changed in <a
+ * href="https://github.com/apache/incubator-gluten/pull/8247";>#8247</a>,
which added the {@code
Review Comment:
Good catch — updated to `apache/gluten`.
##########
gluten-core/src/main/java/org/apache/gluten/memory/memtarget/OverAcquire.java:
##########
@@ -18,29 +18,34 @@
import com.google.common.base.Preconditions;
+/**
+ * Wraps {@code target} and, on each successful {@code borrow}, performs a
preemptive spill probe
+ * against {@code overTarget}.
+ *
+ * <p>The probe asks {@code overTarget} to borrow {@code ratio *
target.usedBytes()} bytes, then
+ * immediately releases them. Because {@code overTarget} shares Spark's memory
pool with {@code
+ * target}, the borrow call forces Spark to spill other memory consumers if
the pool is tight, and
+ * the subsequent repay frees the reservation without holding any actual
memory. The net effect is
+ * that subsequent allocations under {@code target} start with the pool in a
shrunk state and are
+ * less likely to hit an OOM that {@code target} itself cannot spill out of
(for example, a two-step
+ * reservation where step A is spillable but step B is not).
+ *
+ * <p>Historically the over-acquired memory was held for the lifetime of the
reservation as a backup
+ * for OOM; that shape was changed in <a
+ * href="https://github.com/apache/incubator-gluten/pull/8247";>#8247</a>,
which added the {@code
+ * granted >= size} gate and moved the {@code overTarget.repay} to run right
after {@code
+ * overTarget.borrow}. The class no longer holds any over-acquired bytes.
+ */
public class OverAcquire implements MemoryTarget {
// The underlying target.
private final MemoryTarget target;
- // This consumer holds the over-acquired memory.
+ // Probes Spark's memory pool by borrowing / immediately repaying; see the
class Javadoc.
private final MemoryTarget overTarget;
- // The ratio is normally 0.
- //
- // If set to some value other than 0, the consumer will try
- // over-acquire this ratio of memory each time it acquires
- // from Spark.
- //
- // Once OOM, the over-acquired memory will be used as backup.
- //
- // The over-acquire is a general workaround for underling reservation
- // procedures that were not perfectly-designed for spilling. For example,
- // reservation for a two-step procedure: step A is capable for
- // spilling while step B is not. If not reserving enough memory
- // for step B before it's started, it might raise OOM since step A
- // is ended and no longer open for spilling. In this case the
- // over-acquired memory will be used in step B.
+ // Fraction of `target.usedBytes()` used as the probe size on each
successful borrow. When 0
+ // (the default), no probe runs and MemoryTargets#overAcquire returns
`target` directly.
Review Comment:
Right, the default is 0.3. Reworded to describe the behavior ("When set to
0, no probe runs and MemoryTargets#overAcquire returns target unwrapped")
without stating a default, and dropped the backticks.
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