Function dbuf_evict_one

freebsd/contrib/openzfs/module/zfs/dbuf.c:667–700

* Evict the oldest eligible dbuf from the dbuf cache. */

 * Evict the oldest eligible dbuf from the dbuf cache.
 */
static void
dbuf_evict_one(void)
{
	int idx = multilist_get_random_index(dbuf_caches[DB_DBUF_CACHE].cache);
	multilist_sublist_t *mls = multilist_sublist_lock(
	    dbuf_caches[DB_DBUF_CACHE].cache, idx);

	ASSERT(!MUTEX_HELD(&dbuf_evict_lock));

	dmu_buf_impl_t *db = multilist_sublist_tail(mls);
	while (db != NULL && mutex_tryenter(&db->db_mtx) == 0) {
		db = multilist_sublist_prev(mls, db);
	}

	DTRACE_PROBE2(dbuf__evict__one, dmu_buf_impl_t *, db,
	    multilist_sublist_t *, mls);

	if (db != NULL) {
		multilist_sublist_remove(mls, db);
		multilist_sublist_unlock(mls);
		(void) zfs_refcount_remove_many(
		    &dbuf_caches[DB_DBUF_CACHE].size, db->db.db_size, db);
		DBUF_STAT_BUMPDOWN(cache_levels[db->db_level]);
		DBUF_STAT_BUMPDOWN(cache_count);
		DBUF_STAT_DECR(cache_levels_bytes[db->db_level],
		    db->db.db_size);
		ASSERT3U(db->db_caching_status, ==, DB_DBUF_CACHE);
		db->db_caching_status = DB_NO_CACHE;
		dbuf_destroy(db);
		DBUF_STAT_BUMP(cache_total_evicts);
	} else {
		multilist_sublist_unlock(mls);
	}
}

/*
 * The dbuf evict thread is responsible for aging out dbufs from the