linux-kernel - Re: [RFC PATCH 01/31] mm: migrate: Add exchange

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Message-ID: <3AE8BFB7-139B-4312-A0A7-50759BA63362@nvidia.com>
Date:   Thu, 21 Feb 2019 13:25:02 -0800
From:   Zi Yan <ziy@...dia.com>
To:     Jerome Glisse <jglisse@...hat.com>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        John Hubbard <jhubbard@...dia.com>,
        Mark Hairgrove <mhairgrove@...dia.com>,
        Nitin Gupta <nigupta@...dia.com>,
        David Nellans <dnellans@...dia.com>
Subject: Re: [RFC PATCH 01/31] mm: migrate: Add exchange_pages to exchange two
 lists of pages.

On 21 Feb 2019, at 13:10, Jerome Glisse wrote:

> On Fri, Feb 15, 2019 at 02:08:26PM -0800, Zi Yan wrote:
>> From: Zi Yan <ziy@...dia.com>
>>
>> In stead of using two migrate_pages(), a single exchange_pages() would
>> be sufficient and without allocating new pages.
>
> So i believe it would be better to arrange the code differently instead
> of having one function that special case combination, define function for
> each one ie:
>     exchange_anon_to_share()
>     exchange_anon_to_anon()
>     exchange_share_to_share()
>
> Then you could define function to test if a page is in correct states:
>     can_exchange_anon_page() // return true if page can be exchange
>     can_exchange_share_page()
>
> In fact both of this function can be factor out as common helpers with the
> existing migrate code within migrate.c This way we would have one place
> only where we need to handle all the special casing, test and exceptions.
>
> Other than that i could not spot anything obviously wrong but i did not
> spent enough time to check everything. Re-architecturing the code like
> i propose above would make this a lot easier to review i believe.
>

Thank you for reviewing the patch. Your suggestions are very helpful.
I will restructure the code to help people review it.


>> +	from_page_count = page_count(from_page);
>> +	from_map_count = page_mapcount(from_page);
>> +	to_page_count = page_count(to_page);
>> +	to_map_count = page_mapcount(to_page);
>> +	from_flags = from_page->flags;
>> +	to_flags = to_page->flags;
>> +	from_mapping = from_page->mapping;
>> +	to_mapping = to_page->mapping;
>> +	from_index = from_page->index;
>> +	to_index = to_page->index;
>
> Those are not use anywhere ...

Will remove them. Thanks.

--
Best Regards,
Yan Zi