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Date:   Wed, 23 Aug 2023 01:29:55 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Mike Kravetz <mike.kravetz@oracle.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 v2 10/13] mm: Free up a word in the first tail page
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References: <20230816151201.3655946-1-willy@infradead.org>
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 <20230822231741.GC4509@monkey>
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On Tue, Aug 22, 2023 at 04:17:41PM -0700, Mike Kravetz wrote:
> On 08/16/23 16:11, 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.
> 
> hugetlb manually creates and destroys compound pages.  As such it makes
> assumptions about struct page layout.  This breaks hugetlb.  The following
> will allow fix the breakage.
> 
> The hugetlb code is quite fragile when changes like this are made.  I am
> open to suggestions on how we can make this more robust.  Perhaps start
> with a simple set of APIs to create_folio from a set of contiguous pages
> and destroy a folio?

Thanks; those changes look good to me.

I don't have any _immediate_ plans to make your life easier.  When
we get to a memdesc world, it'll all get much easier.