Re: [PATCH 1/2] mm: Avoid putting a bad page back on the LRU v7

[Russ Anderson <rja@sgi.com>]

On Tue, Jul 22, 2008 at 12:42:10PM +1000, Nick Piggin wrote:
> On Saturday 19 July 2008 06:36, Russ Anderson wrote:
> > [PATCH 1/2] mm: Avoid putting a bad page back on the LRU v7
> >
> > Prevent a page with a physical memory error from being placed back
> > on the LRU.  A new page flag (PG_memerror) is added if
> > CONFIG_PAGEFLAGS_EXTENDED is defined.
> >
> > Signed-off-by: Russ Anderson <rja@sgi.com>
> > Reviewed-by: Christoph Lameter <clameter@sgi.com>
> >
> > ---
> >  include/linux/page-flags.h |   18 ++++++++++++++++--
> >  mm/migrate.c               |   31 ++++++++++++++++++++++++++++++-
> >  mm/page_alloc.c            |   13 ++++++++-----
> >  3 files changed, 54 insertions(+), 8 deletions(-)
> >
> > Index: linux/mm/page_alloc.c
> > =================================> > --- linux.orig/mm/page_alloc.c	2008-07-18 15:15:48.000000000 -0500
> > +++ linux/mm/page_alloc.c	2008-07-18 15:16:09.000000000 -0500
> > @@ -602,10 +602,10 @@ static int prep_new_page(struct page *pa
> >  		bad_page(page);
> >
> >  	/*
> > -	 * For now, we report if PG_reserved was found set, but do not
> > -	 * clear it, and do not allocate the page: as a safety net.
> > +	 * For now, we report if PG_reserved or PG_memerror was found set, but
> > +	 * do not clear it, and do not allocate the page: as a safety net.
> >  	 */
> > -	if (PageReserved(page))
> > +	if (PageReserved(page) || PageMemError(page))
> >  		return 1;
> >
> >  	page->flags &= ~(1 << PG_uptodate | 1 << PG_error | 1 << PG_reclaim |
> > @@ -2475,8 +2475,11 @@ static void setup_zone_migrate_reserve(s
> >  			continue;
> >  		page = pfn_to_page(pfn);
> >
> > -		/* Blocks with reserved pages will never free, skip them. */
> > -		if (PageReserved(page))
> > +		/*
> > +		 * Blocks with reserved pages or memory errors will never
> > +		 * free, skip them.
> > +		 */
> > +		if (PageReserved(page) || PageMemError(page))
> >  			continue;
> >
> >  		block_migratetype = get_pageblock_migratetype(page);
> 
> I don't like adding more branches like this into fastpaths like this. It
> would make a lot more sense to me if you just had some private module that
> does the job of isolating the page from the lru and/or elevating their
> refcount so that they do not get put back on freelists.

That is how it works.  If PageMemError is set the migration code
leaves the page with an elevated refcount.  The PageMemError() check
was to avoid reallocating the page was an additional safty net.
I'll pull the checks.

> Migration may need something to perhaps allow migrations of pages not on
> LRU lists but have PageMemError set which is OK, but I really don't like
> adding code and branches to page_alloc.c if possible....
> 
> Thanks,
> Nick

-- 
Russ Anderson, OS RAS/Partitioning Project Lead  
SGI - Silicon Graphics Inc          rja@sgi.com