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Date: Wed, 20 Dec 2023 05:30:33 +0100
From: Johannes Weiner <hannes@cmpxchg.org>
To: Yosry Ahmed <yosryahmed@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Chengming Zhou <zhouchengming@bytedance.com>,
	Nhat Pham <nphamcs@gmail.com>, Chris Li <chriscli@google.com>,
	Seth Jennings <sjenning@redhat.com>,
	Dan Streetman <ddstreet@ieee.org>,
	Vitaly Wool <vitaly.wool@konsulko.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 5/5] mm/zswap: cleanup zswap_reclaim_entry()
Message-ID: <20231220043033.GA23822@cmpxchg.org>
References: <20231213-zswap-dstmem-v1-0-896763369d04@bytedance.com>
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 <20231214142320.f5cf319e619dbb2127c423e9@linux-foundation.org>
 <CAJD7tkaJVB+BoYmcO3MtGD7Ku88Sjk-VAK640h9B-aQzyGPdZQ@mail.gmail.com>
 <20231218140313.GA19167@cmpxchg.org>
 <CAJD7tkbdCv7CMy71UOCefR2Y1BXevJ2eMmYwk+=e=GPcCqn3+w@mail.gmail.com>
 <20231218145815.GA21073@cmpxchg.org>
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On Mon, Dec 18, 2023 at 12:52:40PM -0800, Yosry Ahmed wrote:
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1458,15 +1458,14 @@ static int zswap_writeback_entry(struct
> zswap_entry *entry,
>         page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
>                                 NO_INTERLEAVE_INDEX, &page_was_allocated, true);
>         if (!page) {
> -               /*
> -                * 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.
> -                */
>                 return -ENOMEM;
>         }
> 
> -       /* Found an existing page, we raced with load/swapin */
> +       /*
> +        * Found an existing page, we raced with load/swapin. We generally
> +        * writeback cold pages from zswap, and swapin means the page just
> +        * became hot. Skip this page and let the caller find another one.
> +        */
>         if (!page_was_allocated) {
>                 put_page(page);
>                 return -EEXIST;

ACK, that looks good to me!

Thanks