linux-kernel - Re: [PATCH v5 03/11] mm: thp: introduce separate TTU flag for thp freezing

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Message-Id: <4806dc43-c416-cdb4-f4b5-60553afae036@linux.vnet.ibm.com>
Date:   Fri, 21 Apr 2017 09:59:43 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Zi Yan <zi.yan@...t.com>, n-horiguchi@...jp.nec.com,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, minchan@...nel.org, vbabka@...e.cz,
        mgorman@...hsingularity.net, mhocko@...nel.org,
        khandual@...ux.vnet.ibm.com, zi.yan@...rutgers.edu,
        dnellans@...dia.com
Subject: Re: [PATCH v5 03/11] mm: thp: introduce separate TTU flag for thp
 freezing

On 04/21/2017 02:17 AM, Zi Yan wrote:
> From: Naoya Horiguchi <n-horiguchi@...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@...jp.nec.com>

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