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

[Yosry Ahmed <yosryahmed@google.com>]

On Fri, Jan 19, 2024 at 12:04 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Fri, Jan 19, 2024 at 11:29:42AM -0800, Yosry Ahmed wrote:
> > I see, but it's not clear to me if the xarray is being properly
> > cleaned up in this case.
> >
> > Do we have to call xa_destroy() anyway to make sure everything is
> > cleaned up in the xarray? In that case, we can just do that after the
> > loop.
>
> You do not need to call xa_destroy().  xa_destroy() exists for two
> patterns: first, that you're storing values, not pointers in the tree,
> and you can just delete the tree without leaking memory.  second, that
> you do xas_for_each() { kfree(p); }; xa_destroy();  that's more
> efficient than xas_for_each() { kfree(p); xas_store(NULL); } as it
> batches the freeing of the nodes to the end.
>
> if your code is naturally structured so that you delete the entries
> after freeing them, you have no reason to call xa_destroy().

Thanks for elaborating. Based on this, I believe doing xas_for_each()
{ zswap_free_entry(); }; xa_destroy(); is both closer to the current
code structure and more efficient.