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Index: sys/cam/cam_iosched.c
===================================================================
--- sys/cam/cam_iosched.c
+++ sys/cam/cam_iosched.c
@@ -1496,6 +1496,41 @@
cam_iosched_queue_work(struct cam_iosched_softc *isc, struct bio *bp)
{
+ /*
+ * A BIO_SPEEDUP from the uppper layers means that they have a block
+ * shortage. At the present, this is only sent when we're trying to
+ * allocate blocks, but have a shortage before giving up. bio_length is
+ * the size of their shortage. We will complete just enough BIO_DELETEs
+ * in the queue to satisfy the need. If bio_length is 0, we'll complete
+ * them all. This allows the scheduler to delay BIO_DELETEs to improve
+ * read/write performance without worrying about the upper layers. When
+ * it's possibly a problem, we respond by pretending the BIO_DELETEs
+ * just worked. We can't do anything about the BIO_DELETEs in the
+ * hardware, though. We have to wait for them to complete.
+ */
+ if (bp->bio_cmd == BIO_SPEEDUP) {
+ off_t len;
+ struct bio *nbp;
+
+ len = 0;
+ while (bioq_first(&isc->trim_queue) &&
+ (bp->bio_length == 0 || len < bp->bio_length)) {
+ nbp = bioq_takefirst(&isc->trim_queue);
+ len += nbp->bio_length;
+ nbp->bio_error = 0;
+ biodone(nbp);
+ }
+ if (bp->bio_length > 0) {
+ if (bp->bio_length > len)
+ bp->bio_resid = bp->bio_length - len;
+ else
+ bp->bio_resid = 0;
+ }
+ bp->bio_error = 0;
+ biodone(bp);
+ return;
+ }
+
/*
* If we get a BIO_FLUSH, and we're doing delayed BIO_DELETEs then we
* set the last tick time to one less than the current ticks minus the

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