Re: [PATCH 1/2] mm: zswap.c: add xarray tree to zswap

[Yosry Ahmed]

On Thu, Jan 18, 2024 at 5:52 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Wed, Jan 17, 2024 at 10:20:29PM -0800, Yosry Ahmed wrote:
> > >         /* walk the tree and free everything */
> > >         spin_lock(&tree->lock);
> > > +
> > > +       xas_for_each(&xas, e, ULONG_MAX)
> >
> > Why not use xa_for_each?
>
> xas_for_each() is O(n) while xa_for_each() is O(n log n), as mentioned
> in the fine documentation.  If you don't need to drop the lock while
> in the body of the loop, always prefer xas_for_each().

Thanks for pointing this out. Out of ignorance, I skipped reading the
doc for this one and operated under the general assumption to use xa_*
functions were possible.

The doc also says we should hold either the RCU read lock or the
xa_lock while iterating, we are not doing either here, no?