linux-kernel - Re: [PATCH 2/2] mm: zswap: remove unnecessary tree cleanups in zswap

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Date: Mon, 22 Jan 2024 13:21:48 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, 
	Chris Li <chrisl@...nel.org>, Chengming Zhou <zhouchengming@...edance.com>, 
	Huang Ying <ying.huang@...el.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: zswap: remove unnecessary tree cleanups in zswap_swapoff()

On Fri, Jan 19, 2024 at 6:40 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> During swapoff, try_to_unuse() makes sure that zswap_invalidate() is
> called for all swap entries before zswap_swapoff() is called. This means
> that all zswap entries should already be removed from the tree. Simplify
> zswap_swapoff() by removing the tree cleanup loop, and leaving an
> assertion in its place.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> ---
> Chengming, Chris, I think this should make the tree split and the xarray
> conversion patches simpler (especially the former). If others agree,
> both changes can be rebased on top of this.
> ---
>  mm/zswap.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index f8bc9e0892687..9675c3c27f9d1 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1790,17 +1790,12 @@ void zswap_swapon(int type)
>  void zswap_swapoff(int type)
>  {
>         struct zswap_tree *tree = zswap_trees[type];
> -       struct zswap_entry *entry, *n;
>
>         if (!tree)
>                 return;
>
> -       /* walk the tree and free everything */
> -       spin_lock(&tree->lock);
> -       rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode)
> -               zswap_free_entry(entry);
> -       tree->rbroot = RB_ROOT;
> -       spin_unlock(&tree->lock);
> +       /* try_to_unuse() invalidated all entries already */
> +       WARN_ON_ONCE(!RB_EMPTY_ROOT(&tree->rbroot));
>         kfree(tree);
>         zswap_trees[type] = NULL;
>  }
> --
> 2.43.0.429.g432eaa2c6b-goog
>

Oh man this is sweet! FWIW:
Acked-by: Nhat Pham <nphamcs@...il.com>