linux-kernel - Re: [PATCH 5/5] mm/zswap: cleanup zswap_reclaim

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Date:   Wed, 13 Dec 2023 17:02:25 -0800
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Nhat Pham <nphamcs@...il.com>, Chris Li <chriscli@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 5/5] mm/zswap: cleanup zswap_reclaim_entry()

On Tue, Dec 12, 2023 at 8:18 PM Chengming Zhou
<zhouchengming@...edance.com> wrote:
>
> Also after the common decompress part goes to __zswap_load(), we can
> cleanup the zswap_reclaim_entry() a little.

I think you mean zswap_writeback_entry(), same for the commit title.

>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
>  mm/zswap.c | 23 +++++------------------
>  1 file changed, 5 insertions(+), 18 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 0476e1c553c2..9c709368a0e6 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1449,7 +1449,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         struct page *page;
>         struct mempolicy *mpol;
>         bool page_was_allocated;
> -       int ret;
>         struct writeback_control wbc = {
>                 .sync_mode = WB_SYNC_NONE,
>         };
> @@ -1458,16 +1457,13 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         mpol = get_task_policy(current);
>         page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
>                                 NO_INTERLEAVE_INDEX, &page_was_allocated, true);
> -       if (!page) {
> -               ret = -ENOMEM;
> -               goto fail;
> -       }
> +       if (!page)
> +               return -ENOMEM;
>
>         /* Found an existing page, we raced with load/swapin */
>         if (!page_was_allocated) {
>                 put_page(page);
> -               ret = -EEXIST;
> -               goto fail;
> +               return -EEXIST;
>         }
>
>         /*
> @@ -1481,8 +1477,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) {
>                 spin_unlock(&tree->lock);
>                 delete_from_swap_cache(page_folio(page));
> -               ret = -ENOMEM;
> -               goto fail;
> +               return -ENOMEM;
>         }
>         spin_unlock(&tree->lock);
>
> @@ -1503,15 +1498,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         __swap_writepage(page, &wbc);
>         put_page(page);
>
> -       return ret;
> -
> -fail:
> -       /*
> -        * If we get here because the page is already in swapcache, a
> -        * load may be happening concurrently. It is safe and okay to
> -        * not free the entry. It is also okay to return !0.
> -        */

This comment should be moved above the failure check of
__read_swap_cache_async() above, not completely removed. With that:

Reviewed-by: Yosry Ahmed <yosryahmed@...gle.com>

Feel free to squash this patch into the one creating __zswap_load() or
leaving it as-is.