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Date:   Mon, 28 Sep 2020 20:34:28 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Zi Yan <ziy@nvidia.com>
Cc:     linux-mm@kvack.org,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
        Shakeel Butt <shakeelb@google.com>,
        Yang Shi <shy828301@gmail.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Michal Hocko <mhocko@suse.com>,
        David Hildenbrand <david@redhat.com>,
        William Kucharski <william.kucharski@oracle.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        David Nellans <dnellans@nvidia.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 03/30] mm: thp: use single linked list for THP
 page table page deposit.
Message-ID: <20200928193428.GB30994@casper.infradead.org>
References: <20200928175428.4110504-1-zi.yan@sent.com>
 <20200928175428.4110504-4-zi.yan@sent.com>
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On Mon, Sep 28, 2020 at 01:54:01PM -0400, Zi Yan wrote:
>  		struct {	/* Page table pages */
> -			unsigned long _pt_pad_1;	/* compound_head */
> -			pgtable_t pmd_huge_pte; /* protected by page->ptl */
> +			struct llist_head deposit_head; /* pgtable deposit list head */
> +			struct llist_node deposit_node; /* pgtable deposit list node */

If you're going to use two pointers anyway, you might as well use a
list_head.  But I don't think you need to; you could either use a union
of these or you could use the page_address() of the page to store as
much information as you like!