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Date:   Wed, 22 Jan 2020 08:41:04 +0800
From:   Wei Yang <richardw.yang@linux.intel.com>
To:     Yang Shi <yang.shi@linux.alibaba.com>
Cc:     Wei Yang <richardw.yang@linux.intel.com>,
        akpm@linux-foundation.org, jhubbard@nvidia.com, vbabka@suse.cz,
        cl@linux.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        mhocko@kernel.org
Subject: Re: [Patch v2] mm/migrate.c: also overwrite error when it is bigger
 than zero
Message-ID: <20200122004104.GC11409@richard>
Reply-To: Wei Yang <richardw.yang@linux.intel.com>
References: <20200119065753.21694-1-richardw.yang@linux.intel.com>
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 <6fc3e936-eed0-eb18-ecd8-36dcc4c51218@linux.alibaba.com>
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On Tue, Jan 21, 2020 at 11:30:03AM -0800, Yang Shi wrote:
>
>
>On 1/20/20 5:53 PM, Wei Yang wrote:
>> On Sun, Jan 19, 2020 at 02:57:53PM +0800, Wei Yang wrote:
>> > If we get here after successfully adding page to list, err would be
>> > 1 to indicate the page is queued in the list.
>> > 
>> > Current code has two problems:
>> > 
>> >   * on success, 0 is not returned
>> >   * on error, if add_page_for_migratioin() return 1, and the following err1
>> >     from do_move_pages_to_node() is set, the err1 is not returned since err
>> >     is 1
>> > 
>> > And these behaviors break the user interface.
>> > 
>> > Fixes: e0153fc2c760 ("mm: move_pages: return valid node id in status if the
>> > page is already on the target node").
>> > Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> > 
>> > ---
>> > v2:
>> >   * put more words to explain the error case
>> > ---
>> > mm/migrate.c | 2 +-
>> > 1 file changed, 1 insertion(+), 1 deletion(-)
>> > 
>> > diff --git a/mm/migrate.c b/mm/migrate.c
>> > index 86873b6f38a7..430fdccc733e 100644
>> > --- a/mm/migrate.c
>> > +++ b/mm/migrate.c
>> > @@ -1676,7 +1676,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
>> > 	err1 = do_move_pages_to_node(mm, &pagelist, current_node);
>> > 	if (!err1)
>> > 		err1 = store_status(status, start, current_node, i - start);
>> > -	if (!err)
>> > +	if (err >= 0)
>> > 		err = err1;
>> Ok, as mentioned by Yang and Michal, only err == 0 means no error.
>
>I think Michal means do_move_pages_to_node() only, add_page_for_migration()
>returns 1 on purpose.
>
>But, actually the syscall may still return > 0 value since err1 might be > 0.
>Anyway, this is another regression. The patch itself looks correct to me.
>
>Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
>

Thanks

>
>> 
>> Sounds this regression should be fixed in another place. Let me send out
>> another patch.
>> 
>> > out:
>> > 	return err;
>> > -- 
>> > 2.17.1

-- 
Wei Yang
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