Message-ID: <5576F14C.8080303@suse.cz>
Date: Tue, 09 Jun 2015 15:59:40 +0200
From: Vlastimil Babka <vbabka@suse.cz>
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Hugh Dickins <hughd@google.com>
CC: Dave Hansen <dave.hansen@intel.com>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>, Christoph Lameter <cl@gentwo.org>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Steve Capper <steve.capper@linaro.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>,
        Jerome Marchand <jmarchan@redhat.com>,
        Sasha Levin <sasha.levin@oracle.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCHv6 13/36] mm: drop tail page refcounting
References: <1433351167-125878-1-git-send-email-kirill.shutemov@linux.intel.com> <1433351167-125878-14-git-send-email-kirill.shutemov@linux.intel.com>
In-Reply-To: <1433351167-125878-14-git-send-email-kirill.shutemov@linux.intel.com>
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On 06/03/2015 07:05 PM, Kirill A. Shutemov wrote:
> Tail page refcounting is utterly complicated and painful to support.
>
> It uses ->_mapcount on tail pages to store how many times this page is
> pinned. get_page() bumps ->_mapcount on tail page in addition to
> ->_count on head. This information is required by split_huge_page() to
> be able to distribute pins from head of compound page to tails during
> the split.
>
> We will need ->_mapcount acoount PTE mappings of subpages of the

                            to account

> compound page. We eliminate need in current meaning of ->_mapcount in
> tail pages by forbidding split entirely if the page is pinned.
>
> The only user of tail page refcounting is THP which is marked BROKEN for
> now.
>
> Let's drop all this mess. It makes get_page() and put_page() much
> simpler.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@oracle.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

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