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Date:   Tue, 15 Aug 2023 12:39:58 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     David Hildenbrand <david@redhat.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 9/9] mm: Free up a word in the first tail page
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On Tue, Aug 15, 2023 at 09:59:08AM +0200, David Hildenbrand wrote:
> On 15.08.23 05:26, Matthew Wilcox (Oracle) wrote:
> > Store the folio order in the low byte of the flags word in the first
> > tail page.  This frees up the word that was being used to store the
> > order and dtor bytes previously.
> > 
> 
> Is there still a free flag in page[1] after this change? I need one, at
> least for a prototype I'm working on. (could fallback to page[2], though
> eventually, though)

There are only ~13 flags used in page[1] at this point.  Plenty of
space.