Re: BUG: Bad page state [was: Strange oopses in 2.6.30]

[Johannes Weiner <hannes@cmpxchg.org>]

On Mon, Jun 29, 2009 at 09:41:14AM +0100, Mel Gorman wrote:
> I see the unconditionoal clearing of the flag was merged since but even
> that might be too heavy handed as we are making a locked bit operation
> on every page free. That's unfortunate overhead to incur on every page
> free to handle a situation that should not be occurring at all.

Linus was probably quick to merge it as istr several people hitting
bad_page() triggering.  We should get rid of the locked op, I was just
not 100% sure and chose the safer version.

> > > +		WARN_ONCE(1, KERN_WARNING
> > > +			"Sloppy page flags set process %s at pfn:%05lx\n"
> > > +			"page:%p flags:%p\n",
> > > +			current->comm, page_to_pfn(page),
> > > +			page, (void *)page->flags);
[...]
> > > +		page->flags &= ~PAGE_FLAGS_WARN_AT_FREE;
> > > +	}
> > > +
> > >  	if (unlikely(page_mapcount(page) |
> > >  		(page->mapping != NULL)  |
> > >  		(atomic_read(&page->_count) != 0) |
> > 
> > Howerver, I like this patch concept. this warning is useful and meaningful IMHO.
> > 
> 
> This is a version that is based on top of current mainline that just
> displays the warning. However, I think we should consider changing
> TestClearPageMlocked() back to PageMlocked() and only clearing the flags
> when the unusual condition is encountered.

I have a diff at home that makes this an unlocked
__TestClearPageMlocked(), would you be okay with this?

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