Function zone_fetch_bucket

freebsd/vm/uma_core.c:648–696

* Attempt to satisfy an allocation by retrieving a full bucket from one of the * zone's caches. If a bucket is found the zone is not locked on return. */

 * zone's caches.  If a bucket is found the zone is not locked on return.
 */
static uma_bucket_t
zone_fetch_bucket(uma_zone_t zone, uma_zone_domain_t zdom, bool reclaim)
{
	uma_bucket_t bucket;
	int i;
	bool dtor = false;

	ZDOM_LOCK_ASSERT(zdom);

	if ((bucket = STAILQ_FIRST(&zdom->uzd_buckets)) == NULL)
		return (NULL);

	/* SMR Buckets can not be re-used until readers expire. */
	if ((zone->uz_flags & UMA_ZONE_SMR) != 0 &&
	    bucket->ub_seq != SMR_SEQ_INVALID) {
		if (!smr_poll(zone->uz_smr, bucket->ub_seq, false))
			return (NULL);
		bucket->ub_seq = SMR_SEQ_INVALID;
		dtor = (zone->uz_dtor != NULL) || UMA_ALWAYS_CTORDTOR;
		if (STAILQ_NEXT(bucket, ub_link) != NULL)
			zdom->uzd_seq = STAILQ_NEXT(bucket, ub_link)->ub_seq;
	}
	STAILQ_REMOVE_HEAD(&zdom->uzd_buckets, ub_link);

	KASSERT(zdom->uzd_nitems >= bucket->ub_cnt,
	    ("%s: item count underflow (%ld, %d)",
	    __func__, zdom->uzd_nitems, bucket->ub_cnt));
	KASSERT(bucket->ub_cnt > 0,
	    ("%s: empty bucket in bucket cache", __func__));
	zdom->uzd_nitems -= bucket->ub_cnt;

	/*
	 * Shift the bounds of the current WSS interval to avoid
	 * perturbing the estimate.
	 */
	if (reclaim) {
		zdom->uzd_imin -= lmin(zdom->uzd_imin, bucket->ub_cnt);
		zone_domain_imax_sub(zdom, bucket->ub_cnt);
	} else if (zdom->uzd_imin > zdom->uzd_nitems)
		zdom->uzd_imin = zdom->uzd_nitems;

	ZDOM_UNLOCK(zdom);
	if (dtor)
		for (i = 0; i < bucket->ub_cnt; i++)
			item_dtor(zone, bucket->ub_bucket[i], zone->uz_size,
			    NULL, SKIP_NONE);

	return (bucket);
}

/*
 * Insert a full bucket into the specified cache.  The "ws" parameter indicates