Function cache_alloc

freebsd/vm/uma_core.c:3480–3569

* Replenish an alloc bucket and possibly restore an old one. Called in * a critical section. Returns in a critical section. * * A false return value indicates an allocation failure. * A true return value indicates success and the caller should retry. */

 * A true return value indicates success and the caller should retry.
 */
static __noinline bool
cache_alloc(uma_zone_t zone, uma_cache_t cache, void *udata, int flags)
{
	uma_bucket_t bucket;
	int curdomain, domain;
	bool new;

	CRITICAL_ASSERT(curthread);

	/*
	 * If we have run out of items in our alloc bucket see
	 * if we can switch with the free bucket.
	 *
	 * SMR Zones can't re-use the free bucket until the sequence has
	 * expired.
	 */
	if ((cache_uz_flags(cache) & UMA_ZONE_SMR) == 0 &&
	    cache->uc_freebucket.ucb_cnt != 0) {
		cache_bucket_swap(&cache->uc_freebucket,
		    &cache->uc_allocbucket);
		return (true);
	}

	/*
	 * Discard any empty allocation bucket while we hold no locks.
	 */
	bucket = cache_bucket_unload_alloc(cache);
	critical_exit();

	if (bucket != NULL) {
		KASSERT(bucket->ub_cnt == 0,
		    ("cache_alloc: Entered with non-empty alloc bucket."));
		bucket_free(zone, bucket, udata);
	}

	/*
	 * Attempt to retrieve the item from the per-CPU cache has failed, so
	 * we must go back to the zone.  This requires the zdom lock, so we
	 * must drop the critical section, then re-acquire it when we go back
	 * to the cache.  Since the critical section is released, we may be
	 * preempted or migrate.  As such, make sure not to maintain any
	 * thread-local state specific to the cache from prior to releasing
	 * the critical section.
	 */
	domain = PCPU_GET(domain);
	if ((cache_uz_flags(cache) & UMA_ZONE_ROUNDROBIN) != 0 ||
	    VM_DOMAIN_EMPTY(domain))
		domain = zone_domain_highest(zone, domain);
	bucket = cache_fetch_bucket(zone, cache, domain);
	if (bucket == NULL && zone->uz_bucket_size != 0 && !bucketdisable) {
		bucket = zone_alloc_bucket(zone, udata, domain, flags);
		new = true;
	} else {
		new = false;
	}

	CTR3(KTR_UMA, "uma_zalloc: zone %s(%p) bucket zone returned %p",
	    zone->uz_name, zone, bucket);