linux-ext4 - Re: [PATCH v1 02/14] mm: remove extra ZONE

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Message-ID: <dbd0f54a-ad6c-97a2-17d7-826247424c97@suse.cz>
Date:   Wed, 25 Aug 2021 13:15:20 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Alex Sierra <alex.sierra@....com>, akpm@...ux-foundation.org,
        Felix.Kuehling@....com, linux-mm@...ck.org, rcampbell@...dia.com,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        hch@....de, jgg@...dia.com, jglisse@...hat.com
Subject: Re: [PATCH v1 02/14] mm: remove extra ZONE_DEVICE struct page
 refcount

On 8/25/21 05:48, Alex Sierra wrote:
> From: Ralph Campbell <rcampbell@...dia.com>
> 
> ZONE_DEVICE struct pages have an extra reference count that complicates the
> code for put_page() and several places in the kernel that need to check the
> reference count to see that a page is not being used (gup, compaction,
> migration, etc.). Clean up the code so the reference count doesn't need to
> be treated specially for ZONE_DEVICE.

That's certainly welcome. I just wonder what was the reason to use 1 in the
first place and why it's no longer necessary?