Re: [PATCH] mm: alloc_contig: demote PFN busy message to debug level

[Lucas Stach <l.stach@pengutronix.de>]

Am Freitag, den 02.12.2016, 11:18 +0100 schrieb Vlastimil Babka:
> On 12/02/2016 10:57 AM, Lucas Stach wrote:
> > There are a lot of reasons why a PFN might be busy and unable to be isolated
> > some of which can't really be avoided. This message is spamming the logs when
> > a lot of CMA allocations are happening, causing isolation to happen quite
> > frequently.
> 
> Is this related to Robin's report [1] or you have an independent case of 
> lots of CMA allocations, and in which context are there?
> 
No, I've seen this bug report, but this patch was sitting to be sent out
for a while now.

> > Demote the message to log level, as CMA will just retry the allocation, so
> > there is no need to have this message in the logs. If someone is interested
> > in the failing case, there is a tracepoint to track those failures properly.
> 
> I don't think we should just hide the issue like this, as getting high 
> volume reports from this is also very likely associated with high 
> overhead for the allocations. If it's the generic dma-cma context, like 
> in [1] where it attempts CMA for order-0 allocations, we should first do 
> something about that, before tweaking the logging.
> 
Etnaviv (the driver I maintain) currently does a stupid thing by
allocating and freeing lots of DMA buffers (higher-order) from different
threads. This is causing overhead at the CMA side, but really isn't
something to be handled at the CMA side, but rather Etnaviv must get
more clever about its CMA usage.

Still this message is really disturbing as page isolation failures can
be caused by lots of other reasons like temporarily pinned pages.

Regards,
Lucas

> [1] http://marc.info/?l=linux-mm&m=148053714627617&w=2
> 
> > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > ---
> >  mm/page_alloc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 2b3bf6767d54..b2cfb4074f90 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7398,7 +7398,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
> >
> >  	/* Make sure the range is really isolated. */
> >  	if (test_pages_isolated(outer_start, end, false)) {
> > -		pr_info("%s: [%lx, %lx) PFNs busy\n",
> > +		pr_debug("%s: [%lx, %lx) PFNs busy\n",
> >  			__func__, outer_start, end);
> >  		ret = -EBUSY;
> >  		goto done;
> >
> 
> 


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