linux-kernel - Re: [PATCH v2 1/1] mm/hugetlb: fix memory offline with hugepage size

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Date:   Thu, 22 Sep 2016 15:58:15 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     "'Gerald Schaefer'" <gerald.schaefer@...ibm.com>,
        "'Andrew Morton'" <akpm@...ux-foundation.org>,
        "'Naoya Horiguchi'" <n-horiguchi@...jp.nec.com>
Cc:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        "'Michal Hocko'" <mhocko@...e.cz>,
        "'Kirill A . Shutemov'" <kirill.shutemov@...ux.intel.com>,
        "'Vlastimil Babka'" <vbabka@...e.cz>,
        "'Mike Kravetz'" <mike.kravetz@...cle.com>,
        "'Aneesh Kumar K . V'" <aneesh.kumar@...ux.vnet.ibm.com>,
        "'Martin Schwidefsky'" <schwidefsky@...ibm.com>,
        "'Heiko Carstens'" <heiko.carstens@...ibm.com>,
        "'Dave Hansen'" <dave.hansen@...ux.intel.com>,
        "'Rui Teng'" <rui.teng@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 1/1] mm/hugetlb: fix memory offline with hugepage size > memory block size

> 
> dissolve_free_huge_pages() will either run into the VM_BUG_ON() or a
> list corruption and addressing exception when trying to set a memory
> block offline that is part (but not the first part) of a hugetlb page
> with a size > memory block size.
> 
> When no other smaller hugetlb page sizes are present, the VM_BUG_ON()
> will trigger directly. In the other case we will run into an addressing
> exception later, because dissolve_free_huge_page() will not work on the
> head page of the compound hugetlb page which will result in a NULL
> hstate from page_hstate().
> 
> To fix this, first remove the VM_BUG_ON() because it is wrong, and then
> use the compound head page in dissolve_free_huge_page().
> 
> Also change locking in dissolve_free_huge_page(), so that it only takes
> the lock when actually removing a hugepage.
> 
> Signed-off-by: Gerald Schaefer <gerald.schaefer@...ibm.com>
> ---
Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>