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

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

On Mon, 14 Apr 2008 10:46:47 -0700 (PDT)
Christoph Lameter <clameter@sgi.com> wrote:

> > <snip>
> >         if (PageDirty(page)) {
> >                 clear_page_dirty_for_io(page);
> >                 set_page_dirty(newpage);------------------------(**)
> >         }
> > 
> > ==
> > Then, Uptodate() is copied before set_page_dirty(). 
> > So, "page" is not Uptodate and Dirty when it reaches (**)
> 
> The page will be marked uptodate before we reach ** so its okay in 
> general. If a page is not uptodate then we should not be getting here.
> 
> An !uptodate page is not migratable. Maybe we need to add better checking?
> 
adding check is good but...

I found I can reproduce this. I'd like to chase this a bit more.

following is just a report.
==
a page which caused trouble was
- Dirty, Private, Locked (locked because of migration)
- a file cache of ext3. (maybe)

When I added following check,
==
@@ -648,6 +649,10 @@ static int unmap_and_move(new_page_t get
                        goto move_newpage;
                lock_page(page);
        }
+       /* All caches should be Uptodate before migration.*/
+       if (page_mapping(page) && !PageUptodate(page))
+               goto unlock;
+

        if (PageWriteback(page)) {
                if (!force)
==
A page offlining never ends until I run "echo 3 > /proc/sys/vm/drop_caches".

Once I use drop_caches, memory offlining works very well.
(even under some workload.) If the code I added is bad, plz blame me.

Thanks,
-Kame

 

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