On Tue, Mar 28, 2023 at 2:32 PM Chris Li <chrisl@xxxxxxxxxx> wrote: > > On Tue, Mar 28, 2023 at 02:01:09PM -0700, Yosry Ahmed wrote: > > On Tue, Mar 28, 2023 at 1:50 PM Chris Li <chrisl@xxxxxxxxxx> wrote: > > > > > > On Tue, Mar 28, 2023 at 12:59:31AM -0700, Yosry Ahmed wrote: > > > > > > I don't have a problem with this approach, it is not really clean as > > > > > > we still treat zswap as a swapfile and have to deal with a lot of > > > > > > unnecessary code like swap slots handling and whatnot. > > > > > > > > > > These are existing code? > > > > > > Yes. The ghost swap file are existing code used in Google for many years. > > > > > > > I was referring to the fact that today with zswap being tied to > > > > swapfiles we do some necessary work such as searching for swap slots > > > > during swapout. The initial swap_desc approach aimed to avoid that. > > > > With this minimal ghost swapfile approach we retain this unfavorable > > > > behavior. > > > > > > Can you explain how you can avoid the free swap entry search > > > in the swap descriptor world? > > > > For zswap, in the swap descriptor world, you just need to allocate a > > struct zswap_entry and have the swap descriptor point to it. No need > > for swap slot management since we are not tied to a swapfile and pages > > in zswap do not have a specific position. > > Your swap descriptor will be using one swp_entry_t, which get from the PTE > to lookup, right? That is the swap entry I am talking about. You just > substitute zswap swap entry with the swap descriptor swap entry. > You still need to allocate from the free swap entry space at least once. Oh, you mean the swap ID space. We just need to find an unused ID, we can simply use an allocating xarray (https://docs.kernel.org/core-api/xarray.html#allocating-xarrays). This is simpler than keeping track of swap slots in a swapfile. > > Chris
