linux-ext4 - Re: [PATCH v6 02/13] mm: remove extra ZONE

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Date:   Sun, 15 Aug 2021 17:37:13 +0200
From:   Christoph Hellwig <hch@....de>
To:     Alex Sierra <alex.sierra@....com>
Cc:     akpm@...ux-foundation.org, Felix.Kuehling@....com,
        linux-mm@...ck.org, rcampbell@...dia.com,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        hch@....de, jgg@...dia.com, jglisse@...hat.com,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v6 02/13] mm: remove extra ZONE_DEVICE struct page
 refcount

> 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.