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

Wu Fengguang
2009-06-02T13:53:45Z

On Tue, Jun 02, 2009 at 09:41:26PM +0800, Andi Kleen wrote:
> On Tue, Jun 02, 2009 at 03:24:41PM +0200, Nick Piggin wrote:
> > On Tue, Jun 02, 2009 at 03:25:38PM +0200, Andi Kleen wrote:
> > > On Tue, Jun 02, 2009 at 02:57:13PM +0200, Nick Piggin wrote:
> > > > > > not a big deal and just avoids duplicating code. I attached an
> > > > > > (untested) patch.
> > > > >
> > > > > Thanks. But the function in the patch is not doing the same what
> > > > > the me_pagecache_clean/dirty are doing. For once there is no error
> > > > > checking, as in the second try_to_release_page()
> > > > >
> > > > > Then it doesn't do all the IO error and missing mapping handling.
> > > >
> > > > Obviously I don't mean just use that single call for the entire
> > > > handler. You can set the EIO bit or whatever you like. The
> > > > "error handling" you have there also seems strange. You could
> > > > retain it, but the page is assured to be removed from pagecache.
> > >
> > > The reason this code double checks is that someone could have
> > > a reference (remember we can come in any time) we cannot kill immediately.
> >
> > Can't kill what? The page is gone from pagecache. It may remain
> > other kernel references, but I don't see why this code will
> > consider this as a failure (and not, for example, a raised error
> > count).
>
> It's a failure because the page was still used and not successfully
> isolated.
>
> > + * remove_from_page_cache assumes (mapping && !mapped)
> > + */
> > + if (page_mapping(p) && !page_mapped(p)) {
>
> Ok you're right. That one is not needed. I will remove it.

No! Please read the comment. In fact __remove_from_page_cache() has a

BUG_ON(page_mapped(page));

Or, at least correct that BUG_ON() line together.

Thanks,
Fengguang