linux-kernel - Re: [RFC 2/2] Prevent promotion of page in madvise

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Message-ID: <AANLkTikBJbyd3Kzw0Mip9NkBbBDqf8kes-Z9XvidF1GY@mail.gmail.com>
Date:	Wed, 24 Nov 2010 08:49:49 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [RFC 2/2] Prevent promotion of page in madvise_dontneed

On Tue, Nov 23, 2010 at 6:50 PM, Mel Gorman <mel@....ul.ie> wrote:
> On Mon, Nov 22, 2010 at 02:21:09PM -0800, Andrew Morton wrote:
>> On Sun, 21 Nov 2010 23:30:24 +0900
>> Minchan Kim <minchan.kim@...il.com> wrote:
>>
>> > Now zap_pte_range alwayas promotes pages which are pte_young &&
>> > !VM_SequentialReadHint(vma). But in case of calling MADV_DONTNEED,
>> > it's unnecessary since the page wouldn't use any more.
>> >
>> > If the page is sharred by other processes and it's real working set
>>
>> This patch doesn't actually do anything.  It passes variable `promote'
>> all the way down to unmap_vmas(), but unmap_vmas() doesn't use that new
>> variable.
>>
>> Have a comment fixlet:
>>
>> --- a/mm/memory.c~mm-prevent-promotion-of-page-in-madvise_dontneed-fix
>> +++ a/mm/memory.c
>> @@ -1075,7 +1075,7 @@ static unsigned long unmap_page_range(st
>>   * @end_addr: virtual address at which to end unmapping
>>   * @nr_accounted: Place number of unmapped pages in vm-accountable vma's here
>>   * @details: details of nonlinear truncation or shared cache invalidation
>> - * @promote: whether pages inclued vma would be promoted or not
>> + * @promote: whether pages included in the vma should be promoted or not
>>   *
>>   * Returns the end address of the unmapping (restart addr if interrupted).
>>   *
>> _
>>
>> Also, I'd suggest that we avoid introducing the term "promote".
>
> Promote also has special meaning for huge pages. Demoting or promoting a
> page refers to changing its size. The same applies to the other patch -
> s/demote/deactive/ s/promote/activate/ . Currently this is no confusion
> within the VM but when Andrea's THP patches are merged, it'll become an
> issue.

Thanks for the information.

>
> --
> Mel Gorman
> Part-time Phd Student                          Linux Technology Center
> University of Limerick                         IBM Dublin Software Lab
>



-- 
Kind regards,
Minchan Kim
--
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