linux-kernel - Re: [v2 PATCH 1/2] mm: mempolicy: make the behavior consistent when MPOL_MF_MOVE* and MPOL_MF

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Message-ID: <0a57d280-a56c-ceef-282b-b9dec380c7c7@suse.cz>
Date:   Tue, 16 Jul 2019 10:47:38 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yang Shi <yang.shi@...ux.alibaba.com>, mhocko@...nel.org,
        mgorman@...hsingularity.net, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH 1/2] mm: mempolicy: make the behavior consistent when
 MPOL_MF_MOVE* and MPOL_MF_STRICT were specified

On 7/16/19 10:12 AM, Vlastimil Babka wrote:
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -429,11 +429,14 @@ static inline bool queue_pages_required(struct page *page,
>>  }
>>  
>>  /*
>> - * queue_pages_pmd() has three possible return values:
>> + * queue_pages_pmd() has four possible return values:
>> + * 2 - there is unmovable page, and MPOL_MF_MOVE* & MPOL_MF_STRICT were
>> + *     specified.
>>   * 1 - pages are placed on the right node or queued successfully.
>>   * 0 - THP was split.
> 
> I think if you renumbered these, it would be more consistent with
> queue_pages_pte_range() and simplify the code there.
> 0 - pages on right node/queued
> 1 - unmovable page with right flags specified
> 2 - THP split

Ah, alternatively you could add a boolean to struct queue_pages
accessible from mm_walk, set true to indicate that unmovable page has
been encountered, without propagating it back through special return values.