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

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Message-ID: <20101123095053.GG19571@csn.ul.ie>
Date:	Tue, 23 Nov 2010 09:50:53 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Minchan Kim <minchan.kim@...il.com>, 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 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.

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