Subject: Re: [PATCH v5 03/11] mm: thp: introduce separate TTU flag for thp
 freezing
To: Zi Yan <zi.yan@sent.com>, n-horiguchi@ah.jp.nec.com,
        kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
References: <20170420204752.79703-1-zi.yan@sent.com>
 <20170420204752.79703-4-zi.yan@sent.com>
Cc: akpm@linux-foundation.org, minchan@kernel.org, vbabka@suse.cz,
        mgorman@techsingularity.net, mhocko@kernel.org,
        khandual@linux.vnet.ibm.com, zi.yan@cs.rutgers.edu,
        dnellans@nvidia.com
From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Date: Fri, 21 Apr 2017 09:59:43 +0530
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On 04/21/2017 02:17 AM, Zi Yan wrote:
> From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> 
> TTU_MIGRATION is used to convert pte into migration entry until thp split
> completes. This behavior conflicts with thp migration added later patches,
> so let's introduce a new TTU flag specifically for freezing.
> 
> try_to_unmap() is used both for thp split (via freeze_page()) and page
> migration (via __unmap_and_move()). In freeze_page(), ttu_flag given for
> head page is like below (assuming anonymous thp):
> 
>     (TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED | \
>      TTU_MIGRATION | TTU_SPLIT_HUGE_PMD)
> 
> and ttu_flag given for tail pages is:
> 
>     (TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED | \
>      TTU_MIGRATION)
> 
> __unmap_and_move() calls try_to_unmap() with ttu_flag:
> 
>     (TTU_MIGRATION | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS)
> 
> Now I'm trying to insert a branch for thp migration at the top of
> try_to_unmap_one() like below
> 
> static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>                        unsigned long address, void *arg)
>   {
>           ...
>           if (flags & TTU_MIGRATION) {
>               if (!pvmw.pte && page) {
>                   set_pmd_migration_entry(&pvmw, page);
>                   continue;
>               }
>           }
> 
> , so try_to_unmap() for tail pages called by thp split can go into thp
> migration code path (which converts *pmd* into migration entry), while
> the expectation is to freeze thp (which converts *pte* into migration entry.)
> 
> I detected this failure as a "bad page state" error in a testcase where
> split_huge_page() is called from queue_pages_pte_range().
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

It had Kirril's acked-by (https://patchwork.kernel.org/patch/9416221/)
last time around. Please include again.