linux-kernel - Re: [PATCH] mm, migrate: Check return value of try_to

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Date:   Tue, 03 Mar 2020 14:19:18 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Zi Yan <ziy@...dia.com>, Michal Hocko <mhocko@...nel.org>,
        Minchan Kim <minchan@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] mm, migrate: Check return value of try_to_unmap()

Hi, Hugh,

Hugh Dickins <hughd@...gle.com> writes:
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 3900044cfaa6..981f8374a6ef 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1116,8 +1116,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>>  		/* Establish migration ptes */
>>  		VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma,
>>  				page);
>> -		try_to_unmap(page,
>> -			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
>> +		if (!try_to_unmap(page,
>> +			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS)) {
>> +			rc = -EIO;
>> +			goto out_unlock_both;
>
> No: even if try_to_unmap() says that it did not entirely succeed,
> it may have unmapped some ptes, inserting migration entries in their
> place. Those need to be replaced by proper ptes before the page is
> unlocked, which page_was_mapped 1 and remove_migration_ptes() do;
> but this goto skips those.

Yes.  You are right.  I misunderstand the original code.  Please ignore
this patch.

Best Regards,
Huang, Ying