Re: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v3

[Wu Fengguang <fengguang.wu@intel.com>]

On Tue, Jun 09, 2009 at 06:48:25PM +0800, Nick Piggin wrote:
> On Tue, Jun 09, 2009 at 02:48:55PM +0800, Wu Fengguang wrote:
> > On Mon, Jun 08, 2009 at 10:46:53PM +0800, Nai Xia wrote:
> > > I meant PG_writeback stops writers to index---->struct page mapping.
> > 
> > It's protected by the radix tree RCU locks. Period.
> > 
> > If you are referring to the reverse mapping: page->mapping is procted
> > by PG_lock. No one should make assumption that it won't change under
> > page writeback.
> 
> Well... I think probably PG_writeback should be enough. Phrased another
> way: I think it is a very bad idea to truncate PG_writeback pages out of
> pagecache. Does anything actually do that?

There shall be no one. OK I will follow that convention.. 

But as I stated it is only safe do rely on the fact "no one truncates
PG_writeback pages" in end_writeback_io handlers. And I suspect if
there does exist such a handler, it could be trivially converted to
take the page lock.

Thanks,
Fengguang