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Date:   Sun, 15 Aug 2021 17:37:13 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Alex Sierra <alex.sierra@amd.com>
Cc:     akpm@linux-foundation.org, Felix.Kuehling@amd.com,
        linux-mm@kvack.org, rcampbell@nvidia.com,
        linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        hch@lst.de, jgg@nvidia.com, jglisse@redhat.com,
        John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH v6 02/13] mm: remove extra ZONE_DEVICE struct page
 refcount
Message-ID: <20210815153713.GA32384@lst.de>
References: <20210813063150.2938-1-alex.sierra@amd.com> <20210813063150.2938-3-alex.sierra@amd.com>
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> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8ae31622deef..d48a1f0889d1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1218,7 +1218,7 @@ __maybe_unused struct page *try_grab_compound_head(struct page *page, int refs,
>  static inline __must_check bool try_get_page(struct page *page)
>  {
>  	page = compound_head(page);
> -	if (WARN_ON_ONCE(page_ref_count(page) <= 0))
> +	if (WARN_ON_ONCE(page_ref_count(page) < (int)!is_zone_device_page(page)))

Please avoid the overly long line.  In fact I'd be tempted to just not
bother here and keep the old, more lose check.  Especially given that
John has a patch ready that removes try_get_page entirely.