linux-kernel - Re: [patch 1/2] [PATCH] mm: Save soft-dirty bits on swapped pages

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Date:	Thu, 1 Aug 2013 10:28:14 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	luto@...capital.net, xemul@...allels.com,
	akpm@...ux-foundation.org, mpm@...enic.com,
	xiaoguangrong@...ux.vnet.ibm.com, mtosatti@...hat.com,
	kosaki.motohiro@...il.com, sfr@...b.auug.org.au,
	peterz@...radead.org, aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [patch 1/2] [PATCH] mm: Save soft-dirty bits on swapped pages

On Thu, Aug 01, 2013 at 03:16:32PM +0900, Minchan Kim wrote:
> 
> I don't get it. Could you correct me with below example?
> 
> Process A context
>         try_to_unmap
>                 swp_pte = swp_entry_to_pte /* change generic swp into arch swap */
>                 swp_pte = pte_swp_mksoft_dirty(swp_pte);
>                 set_pte_at(, swp_pte);
> 
> Process A context
>         ..
>         mincore_pte_range
		pte_t pte = *ptep;	<-- local copy of the pte value, in memory it remains the same
						with swap softdirty bit set
>                 pte_to_swp_entry
>                         pte = pte_swp_clear_soft_dirty  <=== 1)
>                         change arch swp with generic swp
>                 mincore_page 
> 
> Process B want to know dirty state of the page
>         ..
>         pagemap_read
>         pte_to_pagemap_entry
>         is_swap_pte
>                 if (pte_swap_soft_dirty(pte)) <=== but failed by 1)
> 
> So, Process B can't get the dirty status from process A's the page.
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