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Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages




On Mon 13-11-17 07:33:13, Ran Wang wrote:
> Hello Michal,
> 
> <snip>
> 
> > Date: Fri, 13 Oct 2017 14:00:12 +0200
> > 
> > From: Michal Hocko <mhocko@xxxxxxxx>
> > 
> > Michael has noticed that the memory offline tries to migrate kernel code
> > pages when doing  echo 0 > /sys/devices/system/memory/memory0/online
> > 
> > The current implementation will fail the operation after several failed page
> > migration attempts but we shouldn't even attempt to migrate that memory
> > and fail right away because this memory is clearly not migrateable. This will
> > become a real problem when we drop the retry loop counter resp. timeout.
> > 
> > The real problem is in has_unmovable_pages in fact. We should fail if there
> > are any non migrateable pages in the area. In orther to guarantee that
> > remove the migrate type checks because MIGRATE_MOVABLE is not
> > guaranteed to contain only migrateable pages. It is merely a heuristic.
> > Similarly MIGRATE_CMA does guarantee that the page allocator doesn't
> > allocate any non-migrateable pages from the block but CMA allocations
> > themselves are unlikely to migrateable. Therefore remove both checks.
> > 
> > Reported-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> > Tested-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> > ---
> >  mm/page_alloc.c | 3 ---
> >  1 file changed, 3 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c index
> > 3badcedf96a7..ad0294ab3e4f 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7355,9 +7355,6 @@ bool has_unmovable_pages(struct zone *zone,
> > struct page *page, int count,
> >  	 */
> >  	if (zone_idx(zone) == ZONE_MOVABLE)
> >  		return false;
> > -	mt = get_pageblock_migratetype(page);
> > -	if (mt == MIGRATE_MOVABLE || is_migrate_cma(mt))
> > -		return false;
> 
> This drop cause DWC3 USB controller fail on initialization with Layerscaper processors
> (such as LS1043A) as below:
> 
> [    2.701437] xhci-hcd xhci-hcd.0.auto: new USB bus registered, assigned bus number 1
> [    2.710949] cma: cma_alloc: alloc failed, req-size: 1 pages, ret: -16
> [    2.717411] xhci-hcd xhci-hcd.0.auto: can't setup: -12
> [    2.727940] xhci-hcd xhci-hcd.0.auto: USB bus 1 deregistered
> [    2.733607] xhci-hcd: probe of xhci-hcd.0.auto failed with error -12
> [    2.739978] xhci-hcd xhci-hcd.1.auto: xHCI Host Controller
> 
> And I notice that someone also reported to you that DWC2 got affected recently,
> so do you have the solution now?

Yes. It should be in linux-next. Have a look at the following email
thread: 
http://lkml.kernel.org/r/20171104082500.qvzbb2kw4suo6cgy@xxxxxxxxxxxxxx

-- 
Michal Hocko
SUSE Labs