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From: Mike Kravetz <mike.kravetz@oracle.com>
To: Yang Shi <yang.shi@linux.alibaba.com>,
	Li Xinhai <lixinhai.lxh@gmail.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>
Cc: akpm <akpm@linux-foundation.org>, mhocko <mhocko@suse.com>,
	n-horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH 2/2] mm/mempolicy: Skip walking HUGETLB vma if MPOL_MF_STRICT is specified alone
Date: Tue, 14 Jan 2020 20:28:31 -0800
Message-ID: <f2a54a74-51f8-1a82-d9f2-54f7652b4dd4@oracle.com> (raw)
In-Reply-To: <7c26d332-c40a-0271-b408-a2079ab00808@linux.alibaba.com>

On 1/14/20 5:24 PM, Yang Shi wrote:
> 
> 
> On 1/14/20 5:07 PM, Mike Kravetz wrote:
>> On 1/14/20 6:09 AM, Li Xinhai wrote:
>>> Add cc to
>>> Yang Shi <yang.shi@linux.alibaba.com>
>>> Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>>> , who has been worked on this part
>>>
>>> On 2020-01-14 at 17:16 Li Xinhai wrote:
>>>> Checking MPOL_MF_STRICT is ignored for HUGETLB vma according to mbind man
>>>> page:
>>>>
>>>> Notes
>>>> MPOL_MF_STRICT is ignored on huge page mappings.
>>>>
>>>> If MPOL_MF_STRICT is specified alone without any MOVE flag, we should
>>>> indicate, from test_walk, that walking this vma should be skipped even if
>>>> there are misplaced pages.
>>>>
>>>> Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
>>>> Cc: Michal Hocko <mhocko@suse.com>
>>>> Cc: Mike Kravetz <mike.kravetz@oracle.com>
>> I do not necessarily disagree with the change.  However, this has made me
>> question a couple things:
>> 1) Why does the man page say MPOL_MF_STRICT is ignored on huge page mappings?
>>     - Is that leftover from the the days when huge page migration was not
>>       supported?
>>     - Is it just because huge page migration is more likely to fail than
>>       base page migration.
>> 2) Does the mbind code function properly when unable to migrate a huge page
>>     MPOL_MF_STRICT is set?  A quick look at the code looks like it returns
>>     EIO.
> 
> I don't know the answer about question #1 I didn't dig into the history. The queue_pages_hugetlb() returns 0 unconditionally, I think this is what "MPOL_MF_STRICT is ignored on huge page mappings" means in code.
> 
> It would return -EIO for base pages or THP as what the manpage describes.
> 

I was thinking about a migration failure after isolation.  This block of
code in do_mbind() after queue_pages_range() and mbind_range().

        if (!err) {
                int nr_failed = 0;

                if (!list_empty(&pagelist)) {
                        WARN_ON_ONCE(flags & MPOL_MF_LAZY);
                        nr_failed = migrate_pages(&pagelist, new_page, NULL,
                                start, MIGRATE_SYNC, MR_MEMPOLICY_MBIND);
                        if (nr_failed)
                                putback_movable_pages(&pagelist);
                }

                if ((ret > 0) || (nr_failed && (flags & MPOL_MF_STRICT)))
                        err = -EIO;

-- 
Mike Kravetz


  reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-14  9:16 [PATCH 1/2] mm/mempolicy: Checking hstate for hugetlbfs page in vma_migratable Li Xinhai
2020-01-14  9:16 ` [PATCH 2/2] mm/mempolicy: Skip walking HUGETLB vma if MPOL_MF_STRICT is specified alone Li Xinhai
2020-01-14 14:09   ` Li Xinhai
2020-01-14 18:27     ` Yang Shi
2020-01-15  1:07     ` Mike Kravetz
2020-01-15  1:24       ` Yang Shi
2020-01-15  4:28         ` Mike Kravetz [this message]
2020-01-15  5:23           ` Yang Shi
2020-01-15  7:36             ` Li Xinhai
2020-01-15 17:16               ` Yang Shi
2020-01-15 21:07       ` Mike Kravetz
2020-01-15 21:30         ` Yang Shi
2020-01-15 21:45           ` Mike Kravetz
2020-01-15 21:59             ` Yang Shi
2020-01-16  8:07               ` HORIGUCHI NAOYA(堀口 直也)
2020-01-16 15:32                 ` Li Xinhai
2020-01-16  7:59         ` Michal Hocko
2020-01-16 19:22           ` Mike Kravetz
2020-01-17  2:32             ` Yang Shi
2020-01-17  2:38             ` Li Xinhai
2020-01-17  7:57               ` Michal Hocko
2020-01-17 12:05                 ` Li Xinhai
2020-01-17 15:20                   ` Michal Hocko
2020-01-17 15:46                     ` Li Xinhai
2020-01-20 12:45                       ` Michal Hocko
2020-01-21 14:15                         ` Li Xinhai
2020-01-21 14:53                           ` Michal Hocko
2020-01-22 13:55                             ` Li Xinhai
2020-01-14 19:12 ` [PATCH 1/2] mm/mempolicy: Checking hstate for hugetlbfs page in vma_migratable Mike Kravetz
2020-01-15  1:25 ` Andrew Morton

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