This is part of a conceptual art discussion about various ideas for generation spaceships. I submitted that the only reason I "weigh" 80 kg is because I have the mass of planet Earth the other side of the soles of my shoes. Hypothetically, if another earth came and hovered 100 feet away from my feet, I ought to be equally attracted to both masses and end up floating in air between them--strangely "weightless".
If a cylinder were to be created in space, it might turn or revolve on its central axis, but there's no reason why soil, water, or myself should "stick" to the inner surface. The cylinder would spin while soil, water, and I would float just as we would inside the space station that is currently in orbit around earth.
No matter how big that O'Neill cylinder was, the mass of the opposing sides would cancel each other out unless the floor was earth thickness and the opposing sides were so far away that the attraction felt was negligible--something along the lines of the radius of Earths orbit around the sun perhaps (structural integrity issues aside).
So, my suggestion is that a generational spaceship can be small (and even centrifugal), but for a gravity substitute you'll need metal boots and a magnetic floor (soil and water still float) or a way to attach engines to an Earth-sized object and propel it to escape velocity. (Who can calculate the thrust force required to do that?)