Re: Warning on memory offline (and possible in usual migration?)

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

I myself want to this patch to be included (to next -mm) and put this under
test. How do you think ? Nick ? Christoph ?

Thanks,
-Kame


On Wed, 23 Apr 2008 02:48:04 +0200
Nick Piggin <npiggin@suse.de> wrote:
> What was happening is that migrate_page_copy wants to transfer the PG_dirty
> bit from old page to new page, so what it would do is set_page_dirty(newpage).
> However set_page_dirty() is used to set the entire page dirty, wheras in
> this case, only part of the page was dirty, and it also was not uptodate.
> 
> Marking the whole page dirty with set_page_dirty would lead to corruption or
> unresolvable conditions -- a dirty && !uptodate page and dirty && !uptodate
> buffers.
> 
> Possibly we could just ClearPageDirty(oldpage); SetPageDirty(newpage);
> however in the interests of keeping the change minimal...
> 
> Signed-off-by: Nick Piggin <npiggin@suse.de>
> ---
> Index: linux-2.6/mm/migrate.c
> ===================================================================
> --- linux-2.6.orig/mm/migrate.c
> +++ linux-2.6/mm/migrate.c
> @@ -383,7 +383,14 @@ static void migrate_page_copy(struct pag
>  
>  	if (PageDirty(page)) {
>  		clear_page_dirty_for_io(page);
> -		set_page_dirty(newpage);
> +		/*
> +		 * Want to mark the page and the radix tree as dirty, and
> +		 * redo the accounting that clear_page_dirty_for_io undid,
> +		 * but we can't use set_page_dirty because that function
> +		 * is actually a signal that all of the page has become dirty.
> +		 * Wheras only part of our page may be dirty.
> +		 */
> +		__set_page_dirty_nobuffers(newpage);
>   	}
>  
>  #ifdef CONFIG_SWAP

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