linux-kernel - Re: [RFC 2/8] Don't allow volatile attribute on THP and KSM

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Date:	Fri, 4 Jan 2013 11:51:05 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC 2/8] Don't allow volatile attribute on THP and KSM

On Thu, Jan 03, 2013 at 08:27:31AM -0800, Dave Hansen wrote:
> On 01/02/2013 08:28 PM, Minchan Kim wrote:
> > VOLATILE imply the the pages in the range isn't working set any more
> > so it's pointless that make them to THP/KSM.
> 
> One of the points of this implementation is that it be able to preserve
> memory contents when there is no pressure.  If those contents happen to
> contain a THP/KSM page, and there's no pressure, it seems like the right
> thing to do is to leave that memory in place.

Indeed. I should have written more cleary,

Current implementation is following as

1. madvised-THP/KSM(1, 10) -> mvolatile(1, 10) -> fail
2. mvolatile(1, 10) -> madvised-THP/KSM(1, 10) -> fail
3. always-THP -> mvolatile -> success -> if memory pressure happens
   -> split_huge_page -> discard.

I think 2,3 makes sense to me but we need to fix 1 in further patches.

> 
> It might be a fair thing to do this in order to keep the implementation
> more sane at the moment.  But, we should make sure there's some good
> text on that in the changelog.

Absolutely, Thanks for pointing out, Dave.

> 
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-- 
Kind regards,
Minchan Kim
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